diff --git a/.flake8 b/.flake8
index ed931638..29227d4c 100644
--- a/.flake8
+++ b/.flake8
@@ -26,6 +26,7 @@ exclude =
   *_pb2.py
 
   # Standard linting exemptions.
+  **/.nox/**
   __pycache__,
   .git,
   *.pyc,
diff --git a/.github/header-checker-lint.yml b/.github/header-checker-lint.yml
new file mode 100644
index 00000000..fc281c05
--- /dev/null
+++ b/.github/header-checker-lint.yml
@@ -0,0 +1,15 @@
+{"allowedCopyrightHolders": ["Google LLC"],
+ "allowedLicenses": ["Apache-2.0", "MIT", "BSD-3"],
+ "ignoreFiles": ["**/requirements.txt", "**/requirements-test.txt"],
+ "sourceFileExtensions": [
+ 	"ts", 
+ 	"js", 
+ 	"java", 
+ 	"sh", 
+ 	"Dockerfile", 
+ 	"yaml", 
+ 	"py",
+ 	"html",
+ 	"txt"
+ ]
+}
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index b9daa52f..b4243ced 100644
--- a/.gitignore
+++ b/.gitignore
@@ -50,8 +50,10 @@ docs.metadata
 
 # Virtual environment
 env/
+
+# Test logs
 coverage.xml
-sponge_log.xml
+*sponge_log.xml
 
 # System test environment variables.
 system_tests/local_test_setup
diff --git a/.kokoro/build.sh b/.kokoro/build.sh
index 58504723..84370c6a 100755
--- a/.kokoro/build.sh
+++ b/.kokoro/build.sh
@@ -15,7 +15,11 @@
 
 set -eo pipefail
 
-cd github/python-texttospeech
+if [[ -z "${PROJECT_ROOT:-}" ]]; then
+    PROJECT_ROOT="github/python-texttospeech"
+fi
+
+cd "${PROJECT_ROOT}"
 
 # Disable buffering, so that the logs stream through.
 export PYTHONUNBUFFERED=1
@@ -30,16 +34,26 @@ export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
 export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
 
 # Remove old nox
-python3.6 -m pip uninstall --yes --quiet nox-automation
+python3 -m pip uninstall --yes --quiet nox-automation
 
 # Install nox
-python3.6 -m pip install --upgrade --quiet nox
-python3.6 -m nox --version
+python3 -m pip install --upgrade --quiet nox
+python3 -m nox --version
+
+# If this is a continuous build, send the test log to the FlakyBot.
+# See https://github.com/googleapis/repo-automation-bots/tree/master/packages/flakybot.
+if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"continuous"* ]]; then
+  cleanup() {
+    chmod +x $KOKORO_GFILE_DIR/linux_amd64/flakybot
+    $KOKORO_GFILE_DIR/linux_amd64/flakybot
+  }
+  trap cleanup EXIT HUP
+fi
 
 # If NOX_SESSION is set, it only runs the specified session,
 # otherwise run all the sessions.
 if [[ -n "${NOX_SESSION:-}" ]]; then
-    python3.6 -m nox -s "${NOX_SESSION:-}"
+    python3 -m nox -s ${NOX_SESSION:-}
 else
-    python3.6 -m nox
+    python3 -m nox
 fi
diff --git a/.kokoro/docs/common.cfg b/.kokoro/docs/common.cfg
index 35fcc764..2d11b517 100644
--- a/.kokoro/docs/common.cfg
+++ b/.kokoro/docs/common.cfg
@@ -30,7 +30,7 @@ env_vars: {
 
 env_vars: {
     key: "V2_STAGING_BUCKET"
-    value: "docs-staging-v2-staging"
+    value: "docs-staging-v2"
 }
 
 # It will upload the docker image after successful builds.
diff --git a/.kokoro/docs/docs-presubmit.cfg b/.kokoro/docs/docs-presubmit.cfg
index 11181078..0658d129 100644
--- a/.kokoro/docs/docs-presubmit.cfg
+++ b/.kokoro/docs/docs-presubmit.cfg
@@ -15,3 +15,14 @@ env_vars: {
     key: "TRAMPOLINE_IMAGE_UPLOAD"
     value: "false"
 }
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-texttospeech/.kokoro/build.sh"
+}
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "docs docfx"
+}
diff --git a/.kokoro/populate-secrets.sh b/.kokoro/populate-secrets.sh
new file mode 100755
index 00000000..f5251425
--- /dev/null
+++ b/.kokoro/populate-secrets.sh
@@ -0,0 +1,43 @@
+#!/bin/bash
+# Copyright 2020 Google LLC.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+function now { date +"%Y-%m-%d %H:%M:%S" | tr -d '\n' ;}
+function msg { println "$*" >&2 ;}
+function println { printf '%s\n' "$(now) $*" ;}
+
+
+# Populates requested secrets set in SECRET_MANAGER_KEYS from service account:
+# kokoro-trampoline@cloud-devrel-kokoro-resources.iam.gserviceaccount.com
+SECRET_LOCATION="${KOKORO_GFILE_DIR}/secret_manager"
+msg "Creating folder on disk for secrets: ${SECRET_LOCATION}"
+mkdir -p ${SECRET_LOCATION}
+for key in $(echo ${SECRET_MANAGER_KEYS} | sed "s/,/ /g")
+do
+  msg "Retrieving secret ${key}"
+  docker run --entrypoint=gcloud \
+    --volume=${KOKORO_GFILE_DIR}:${KOKORO_GFILE_DIR} \
+    gcr.io/google.com/cloudsdktool/cloud-sdk \
+    secrets versions access latest \
+    --project cloud-devrel-kokoro-resources \
+    --secret ${key} > \
+    "${SECRET_LOCATION}/${key}"
+  if [[ $? == 0 ]]; then
+    msg "Secret written to ${SECRET_LOCATION}/${key}"
+  else
+    msg "Error retrieving secret ${key}"
+  fi
+done
diff --git a/.kokoro/release/common.cfg b/.kokoro/release/common.cfg
index 25ed0e04..09630f49 100644
--- a/.kokoro/release/common.cfg
+++ b/.kokoro/release/common.cfg
@@ -23,42 +23,18 @@ env_vars: {
     value: "github/python-texttospeech/.kokoro/release.sh"
 }
 
-# Fetch the token needed for reporting release status to GitHub
-before_action {
-  fetch_keystore {
-    keystore_resource {
-      keystore_config_id: 73713
-      keyname: "yoshi-automation-github-key"
-    }
-  }
-}
-
-# Fetch PyPI password
-before_action {
-  fetch_keystore {
-    keystore_resource {
-      keystore_config_id: 73713
-      keyname: "google_cloud_pypi_password"
-    }
-  }
-}
-
-# Fetch magictoken to use with Magic Github Proxy 
-before_action {
-  fetch_keystore {
-    keystore_resource {
-      keystore_config_id: 73713
-      keyname: "releasetool-magictoken"
-    }
-  }
+# Fetch PyPI password	
+before_action {	
+  fetch_keystore {	
+    keystore_resource {	
+      keystore_config_id: 73713	
+      keyname: "google_cloud_pypi_password"	
+    }	
+  }	
 }
 
-# Fetch api key to use with Magic Github Proxy 
-before_action {
-  fetch_keystore {
-    keystore_resource {
-      keystore_config_id: 73713
-      keyname: "magic-github-proxy-api-key"
-    }
-  }
-}
+# Tokens needed to report release status back to GitHub
+env_vars: {
+  key: "SECRET_MANAGER_KEYS"
+  value: "releasetool-publish-reporter-app,releasetool-publish-reporter-googleapis-installation,releasetool-publish-reporter-pem"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.6/common.cfg b/.kokoro/samples/python3.6/common.cfg
index b508c66b..ef2b0243 100644
--- a/.kokoro/samples/python3.6/common.cfg
+++ b/.kokoro/samples/python3.6/common.cfg
@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.6"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py36"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-texttospeech/.kokoro/test-samples.sh"
diff --git a/.kokoro/samples/python3.7/common.cfg b/.kokoro/samples/python3.7/common.cfg
index 48f4103b..83138745 100644
--- a/.kokoro/samples/python3.7/common.cfg
+++ b/.kokoro/samples/python3.7/common.cfg
@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.7"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py37"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-texttospeech/.kokoro/test-samples.sh"
diff --git a/.kokoro/samples/python3.8/common.cfg b/.kokoro/samples/python3.8/common.cfg
index 4d1900a8..b01fc11d 100644
--- a/.kokoro/samples/python3.8/common.cfg
+++ b/.kokoro/samples/python3.8/common.cfg
@@ -13,6 +13,12 @@ env_vars: {
     value: "py-3.8"
 }
 
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py38"
+}
+
 env_vars: {
     key: "TRAMPOLINE_BUILD_FILE"
     value: "github/python-texttospeech/.kokoro/test-samples.sh"
diff --git a/.kokoro/test-samples.sh b/.kokoro/test-samples.sh
index 51a72c73..54e162a1 100755
--- a/.kokoro/test-samples.sh
+++ b/.kokoro/test-samples.sh
@@ -28,6 +28,12 @@ if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"periodic"* ]]; then
     git checkout $LATEST_RELEASE
 fi
 
+# Exit early if samples directory doesn't exist
+if [ ! -d "./samples" ]; then
+  echo "No tests run. `./samples` not found"
+  exit 0
+fi
+
 # Disable buffering, so that the logs stream through.
 export PYTHONUNBUFFERED=1
 
@@ -81,11 +87,11 @@ for file in samples/**/requirements.txt; do
     python3.6 -m nox -s "$RUN_TESTS_SESSION"
     EXIT=$?
 
-    # If this is a periodic build, send the test log to the Build Cop Bot.
-    # See https://github.com/googleapis/repo-automation-bots/tree/master/packages/buildcop.
+    # If this is a periodic build, send the test log to the FlakyBot.
+    # See https://github.com/googleapis/repo-automation-bots/tree/master/packages/flakybot.
     if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"periodic"* ]]; then
-      chmod +x $KOKORO_GFILE_DIR/linux_amd64/buildcop
-      $KOKORO_GFILE_DIR/linux_amd64/buildcop
+      chmod +x $KOKORO_GFILE_DIR/linux_amd64/flakybot
+      $KOKORO_GFILE_DIR/linux_amd64/flakybot
     fi
 
     if [[ $EXIT -ne 0 ]]; then
@@ -101,4 +107,4 @@ cd "$ROOT"
 # Workaround for Kokoro permissions issue: delete secrets
 rm testing/{test-env.sh,client-secrets.json,service-account.json}
 
-exit "$RTN"
\ No newline at end of file
+exit "$RTN"
diff --git a/.kokoro/trampoline.sh b/.kokoro/trampoline.sh
index e8c4251f..f39236e9 100755
--- a/.kokoro/trampoline.sh
+++ b/.kokoro/trampoline.sh
@@ -15,9 +15,14 @@
 
 set -eo pipefail
 
-python3 "${KOKORO_GFILE_DIR}/trampoline_v1.py"  || ret_code=$?
+# Always run the cleanup script, regardless of the success of bouncing into
+# the container.
+function cleanup() {
+    chmod +x ${KOKORO_GFILE_DIR}/trampoline_cleanup.sh
+    ${KOKORO_GFILE_DIR}/trampoline_cleanup.sh
+    echo "cleanup";
+}
+trap cleanup EXIT
 
-chmod +x ${KOKORO_GFILE_DIR}/trampoline_cleanup.sh
-${KOKORO_GFILE_DIR}/trampoline_cleanup.sh || true
-
-exit ${ret_code}
+$(dirname $0)/populate-secrets.sh # Secret Manager secrets.
+python3 "${KOKORO_GFILE_DIR}/trampoline_v1.py"
\ No newline at end of file
diff --git a/.kokoro/trampoline_v2.sh b/.kokoro/trampoline_v2.sh
index 719bcd5b..4af6cdc2 100755
--- a/.kokoro/trampoline_v2.sh
+++ b/.kokoro/trampoline_v2.sh
@@ -159,7 +159,7 @@ if [[ -n "${KOKORO_BUILD_ID:-}" ]]; then
 	"KOKORO_GITHUB_COMMIT"
 	"KOKORO_GITHUB_PULL_REQUEST_NUMBER"
 	"KOKORO_GITHUB_PULL_REQUEST_COMMIT"
-	# For Build Cop Bot
+	# For FlakyBot
 	"KOKORO_GITHUB_COMMIT_URL"
 	"KOKORO_GITHUB_PULL_REQUEST_URL"
     )
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 00000000..a9024b15
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,17 @@
+# See https://pre-commit.com for more information
+# See https://pre-commit.com/hooks.html for more hooks
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.4.0
+    hooks:
+    -   id: trailing-whitespace
+    -   id: end-of-file-fixer
+    -   id: check-yaml
+-   repo: https://github.com/psf/black
+    rev: 19.10b0
+    hooks:
+    - id: black
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: 3.8.4
+    hooks:
+    - id: flake8
diff --git a/.trampolinerc b/.trampolinerc
index 995ee291..383b6ec8 100644
--- a/.trampolinerc
+++ b/.trampolinerc
@@ -24,6 +24,7 @@ required_envvars+=(
 pass_down_envvars+=(
     "STAGING_BUCKET"
     "V2_STAGING_BUCKET"
+    "NOX_SESSION"
 )
 
 # Prevent unintentional override on the default image.
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
index b3d1f602..039f4368 100644
--- a/CODE_OF_CONDUCT.md
+++ b/CODE_OF_CONDUCT.md
@@ -1,44 +1,95 @@
 <!-- # Generated by synthtool. DO NOT EDIT! !-->
-# Contributor Code of Conduct
+# Code of Conduct
 
-As contributors and maintainers of this project,
-and in the interest of fostering an open and welcoming community,
-we pledge to respect all people who contribute through reporting issues,
-posting feature requests, updating documentation,
-submitting pull requests or patches, and other activities.
+## Our Pledge
 
-We are committed to making participation in this project
-a harassment-free experience for everyone,
-regardless of level of experience, gender, gender identity and expression,
-sexual orientation, disability, personal appearance,
-body size, race, ethnicity, age, religion, or nationality.
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, gender identity and expression, level of
+experience, education, socio-economic status, nationality, personal appearance,
+race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+*   Using welcoming and inclusive language
+*   Being respectful of differing viewpoints and experiences
+*   Gracefully accepting constructive criticism
+*   Focusing on what is best for the community
+*   Showing empathy towards other community members
 
 Examples of unacceptable behavior by participants include:
 
-* The use of sexualized language or imagery
-* Personal attacks
-* Trolling or insulting/derogatory comments
-* Public or private harassment
-* Publishing other's private information,
-such as physical or electronic
-addresses, without explicit permission
-* Other unethical or unprofessional conduct.
+*   The use of sexualized language or imagery and unwelcome sexual attention or
+    advances
+*   Trolling, insulting/derogatory comments, and personal or political attacks
+*   Public or private harassment
+*   Publishing others' private information, such as a physical or electronic
+    address, without explicit permission
+*   Other conduct which could reasonably be considered inappropriate in a
+    professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
 
 Project maintainers have the right and responsibility to remove, edit, or reject
-comments, commits, code, wiki edits, issues, and other contributions
-that are not aligned to this Code of Conduct.
-By adopting this Code of Conduct,
-project maintainers commit themselves to fairly and consistently
-applying these principles to every aspect of managing this project.
-Project maintainers who do not follow or enforce the Code of Conduct
-may be permanently removed from the project team.
-
-This code of conduct applies both within project spaces and in public spaces
-when an individual is representing the project or its community.
-
-Instances of abusive, harassing, or otherwise unacceptable behavior
-may be reported by opening an issue
-or contacting one or more of the project maintainers.
-
-This Code of Conduct is adapted from the [Contributor Covenant](http://contributor-covenant.org), version 1.2.0,
-available at [http://contributor-covenant.org/version/1/2/0/](http://contributor-covenant.org/version/1/2/0/)
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, or to ban temporarily or permanently any
+contributor for other behaviors that they deem inappropriate, threatening,
+offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+This Code of Conduct also applies outside the project spaces when the Project
+Steward has a reasonable belief that an individual's behavior may have a
+negative impact on the project or its community.
+
+## Conflict Resolution
+
+We do not believe that all conflict is bad; healthy debate and disagreement
+often yield positive results. However, it is never okay to be disrespectful or
+to engage in behavior that violates the project’s code of conduct.
+
+If you see someone violating the code of conduct, you are encouraged to address
+the behavior directly with those involved. Many issues can be resolved quickly
+and easily, and this gives people more control over the outcome of their
+dispute. If you are unable to resolve the matter for any reason, or if the
+behavior is threatening or harassing, report it. We are dedicated to providing
+an environment where participants feel welcome and safe.
+
+
+Reports should be directed to *googleapis-stewards@google.com*, the
+Project Steward(s) for *Google Cloud Client Libraries*. It is the Project Steward’s duty to
+receive and address reported violations of the code of conduct. They will then
+work with a committee consisting of representatives from the Open Source
+Programs Office and the Google Open Source Strategy team. If for any reason you
+are uncomfortable reaching out to the Project Steward, please email
+opensource@google.com.
+
+We will investigate every complaint, but you may not receive a direct response.
+We will use our discretion in determining when and how to follow up on reported
+incidents, which may range from not taking action to permanent expulsion from
+the project and project-sponsored spaces. We will notify the accused of the
+report and provide them an opportunity to discuss it before any action is taken.
+The identity of the reporter will be omitted from the details of the report
+supplied to the accused. In potentially harmful situations, such as ongoing
+harassment or threats to anyone's safety, we may take action without notice.
+
+## Attribution
+
+This Code of Conduct is adapted from the Contributor Covenant, version 1.4,
+available at
+https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
\ No newline at end of file
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
index 98f6a6be..ce1c3ce4 100644
--- a/CONTRIBUTING.rst
+++ b/CONTRIBUTING.rst
@@ -21,8 +21,8 @@ In order to add a feature:
 - The feature must be documented in both the API and narrative
   documentation.
 
-- The feature must work fully on the following CPython versions:  2.7,
-  3.5, 3.6, 3.7 and 3.8 on both UNIX and Windows.
+- The feature must work fully on the following CPython versions:
+  3.6, 3.7, 3.8 and 3.9 on both UNIX and Windows.
 
 - The feature must not add unnecessary dependencies (where
   "unnecessary" is of course subjective, but new dependencies should
@@ -70,9 +70,14 @@ We use `nox <https://nox.readthedocs.io/en/latest/>`__ to instrument our tests.
 - To test your changes, run unit tests with ``nox``::
 
     $ nox -s unit-2.7
-    $ nox -s unit-3.7
+    $ nox -s unit-3.8
     $ ...
 
+- Args to pytest can be passed through the nox command separated by a `--`. For
+  example, to run a single test::
+
+    $ nox -s unit-3.8 -- -k <name of test>
+
   .. note::
 
     The unit tests and system tests are described in the
@@ -80,25 +85,6 @@ We use `nox <https://nox.readthedocs.io/en/latest/>`__ to instrument our tests.
 
 .. nox: https://pypi.org/project/nox/
 
-Note on Editable Installs / Develop Mode
-========================================
-
-- As mentioned previously, using ``setuptools`` in `develop mode`_
-  or a ``pip`` `editable install`_ is not possible with this
-  library. This is because this library uses `namespace packages`_.
-  For context see `Issue #2316`_ and the relevant `PyPA issue`_.
-
-  Since ``editable`` / ``develop`` mode can't be used, packages
-  need to be installed directly. Hence your changes to the source
-  tree don't get incorporated into the **already installed**
-  package.
-
-.. _namespace packages: https://www.python.org/dev/peps/pep-0420/
-.. _Issue #2316: https://github.com/GoogleCloudPlatform/google-cloud-python/issues/2316
-.. _PyPA issue: https://github.com/pypa/packaging-problems/issues/12
-.. _develop mode: https://setuptools.readthedocs.io/en/latest/setuptools.html#development-mode
-.. _editable install: https://pip.pypa.io/en/stable/reference/pip_install/#editable-installs
-
 *****************************************
 I'm getting weird errors... Can you help?
 *****************************************
@@ -112,8 +98,12 @@ On Debian/Ubuntu::
 ************
 Coding Style
 ************
+- We use the automatic code formatter ``black``. You can run it using
+  the nox session ``blacken``. This will eliminate many lint errors. Run via::
 
-- PEP8 compliance, with exceptions defined in the linter configuration.
+   $ nox -s blacken
+
+- PEP8 compliance is required, with exceptions defined in the linter configuration.
   If you have ``nox`` installed, you can test that you have not introduced
   any non-compliant code via::
 
@@ -130,6 +120,16 @@ Coding Style
   should point to the official ``googleapis`` checkout and the
   the branch should be the main branch on that remote (``master``).
 
+- This repository contains configuration for the
+  `pre-commit <https://pre-commit.com/>`__ tool, which automates checking
+  our linters during a commit.  If you have it installed on your ``$PATH``,
+  you can enable enforcing those checks via:
+
+.. code-block:: bash
+
+   $ pre-commit install
+   pre-commit installed at .git/hooks/pre-commit
+
 Exceptions to PEP8:
 
 - Many unit tests use a helper method, ``_call_fut`` ("FUT" is short for
@@ -142,13 +142,18 @@ Running System Tests
 
 - To run system tests, you can execute::
 
-   $ nox -s system-3.7
+   # Run all system tests
+   $ nox -s system-3.8
    $ nox -s system-2.7
 
+   # Run a single system test
+   $ nox -s system-3.8 -- -k <name of test>
+
+
   .. note::
 
       System tests are only configured to run under Python 2.7 and
-      Python 3.7. For expediency, we do not run them in older versions
+      Python 3.8. For expediency, we do not run them in older versions
       of Python 3.
 
   This alone will not run the tests. You'll need to change some local
@@ -211,25 +216,24 @@ Supported Python Versions
 
 We support:
 
--  `Python 3.5`_
 -  `Python 3.6`_
 -  `Python 3.7`_
 -  `Python 3.8`_
+-  `Python 3.9`_
 
-.. _Python 3.5: https://docs.python.org/3.5/
 .. _Python 3.6: https://docs.python.org/3.6/
 .. _Python 3.7: https://docs.python.org/3.7/
 .. _Python 3.8: https://docs.python.org/3.8/
+.. _Python 3.9: https://docs.python.org/3.9/
 
 
 Supported versions can be found in our ``noxfile.py`` `config`_.
 
 .. _config: https://github.com/googleapis/python-texttospeech/blob/master/noxfile.py
 
-Python 2.7 support is deprecated. All code changes should maintain Python 2.7 compatibility until January 1, 2020.
 
 We also explicitly decided to support Python 3 beginning with version
-3.5. Reasons for this include:
+3.6. Reasons for this include:
 
 -  Encouraging use of newest versions of Python 3
 -  Taking the lead of `prominent`_ open-source `projects`_
diff --git a/LICENSE b/LICENSE
index a8ee855d..d6456956 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,7 @@
-                            Apache License
+
+                                 Apache License
                            Version 2.0, January 2004
-                        https://www.apache.org/licenses/
+                        http://www.apache.org/licenses/
 
    TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
 
@@ -192,7 +193,7 @@
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at
 
-       https://www.apache.org/licenses/LICENSE-2.0
+       http://www.apache.org/licenses/LICENSE-2.0
 
    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
diff --git a/MANIFEST.in b/MANIFEST.in
index e9e29d12..e783f4c6 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -16,10 +16,10 @@
 
 # Generated by synthtool. DO NOT EDIT!
 include README.rst LICENSE
-recursive-include google *.json *.proto
+recursive-include google *.json *.proto py.typed
 recursive-include tests *
 global-exclude *.py[co]
 global-exclude __pycache__
 
 # Exclude scripts for samples readmegen
-prune scripts/readme-gen
\ No newline at end of file
+prune scripts/readme-gen
diff --git a/docs/_static/custom.css b/docs/_static/custom.css
index 0abaf229..bcd37bbd 100644
--- a/docs/_static/custom.css
+++ b/docs/_static/custom.css
@@ -1,4 +1,9 @@
 div#python2-eol {
 	border-color: red;
 	border-width: medium;
-} 
\ No newline at end of file
+} 
+
+/* Ensure minimum width for 'Parameters' / 'Returns' column */
+dl.field-list > dt {
+    min-width: 100px
+}
diff --git a/docs/conf.py b/docs/conf.py
index b30742a4..acbea801 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -39,6 +39,7 @@
     "sphinx.ext.autosummary",
     "sphinx.ext.intersphinx",
     "sphinx.ext.coverage",
+    "sphinx.ext.doctest",
     "sphinx.ext.napoleon",
     "sphinx.ext.todo",
     "sphinx.ext.viewcode",
@@ -344,10 +345,11 @@
 
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
-    "python": ("http://python.readthedocs.org/en/latest/", None),
-    "google-auth": ("https://google-auth.readthedocs.io/en/stable", None),
+    "python": ("https://python.readthedocs.org/en/latest/", None),
+    "google-auth": ("https://googleapis.dev/python/google-auth/latest/", None),
     "google.api_core": ("https://googleapis.dev/python/google-api-core/latest/", None,),
-    "grpc": ("https://grpc.io/grpc/python/", None),
+    "grpc": ("https://grpc.github.io/grpc/python/", None),
+    "proto-plus": ("https://proto-plus-python.readthedocs.io/en/latest/", None),
 }
 
 
diff --git a/docs/texttospeech_v1/services.rst b/docs/texttospeech_v1/services.rst
index 23799bc0..a77f8167 100644
--- a/docs/texttospeech_v1/services.rst
+++ b/docs/texttospeech_v1/services.rst
@@ -1,6 +1,6 @@
 Services for Google Cloud Texttospeech v1 API
 =============================================
+.. toctree::
+    :maxdepth: 2
 
-.. automodule:: google.cloud.texttospeech_v1.services.text_to_speech
-    :members:
-    :inherited-members:
+    text_to_speech
diff --git a/docs/texttospeech_v1/text_to_speech.rst b/docs/texttospeech_v1/text_to_speech.rst
new file mode 100644
index 00000000..2ad3a8e9
--- /dev/null
+++ b/docs/texttospeech_v1/text_to_speech.rst
@@ -0,0 +1,6 @@
+TextToSpeech
+------------------------------
+
+.. automodule:: google.cloud.texttospeech_v1.services.text_to_speech
+    :members:
+    :inherited-members:
diff --git a/docs/texttospeech_v1/types.rst b/docs/texttospeech_v1/types.rst
index 626ff0d3..646ebdc9 100644
--- a/docs/texttospeech_v1/types.rst
+++ b/docs/texttospeech_v1/types.rst
@@ -3,3 +3,5 @@ Types for Google Cloud Texttospeech v1 API
 
 .. automodule:: google.cloud.texttospeech_v1.types
     :members:
+    :undoc-members:
+    :show-inheritance:
diff --git a/docs/texttospeech_v1beta1/services.rst b/docs/texttospeech_v1beta1/services.rst
index ddf8876a..67852d05 100644
--- a/docs/texttospeech_v1beta1/services.rst
+++ b/docs/texttospeech_v1beta1/services.rst
@@ -1,6 +1,6 @@
 Services for Google Cloud Texttospeech v1beta1 API
 ==================================================
+.. toctree::
+    :maxdepth: 2
 
-.. automodule:: google.cloud.texttospeech_v1beta1.services.text_to_speech
-    :members:
-    :inherited-members:
+    text_to_speech
diff --git a/docs/texttospeech_v1beta1/text_to_speech.rst b/docs/texttospeech_v1beta1/text_to_speech.rst
new file mode 100644
index 00000000..8521daf8
--- /dev/null
+++ b/docs/texttospeech_v1beta1/text_to_speech.rst
@@ -0,0 +1,6 @@
+TextToSpeech
+------------------------------
+
+.. automodule:: google.cloud.texttospeech_v1beta1.services.text_to_speech
+    :members:
+    :inherited-members:
diff --git a/docs/texttospeech_v1beta1/types.rst b/docs/texttospeech_v1beta1/types.rst
index 84c63fc8..0306c6cd 100644
--- a/docs/texttospeech_v1beta1/types.rst
+++ b/docs/texttospeech_v1beta1/types.rst
@@ -3,3 +3,5 @@ Types for Google Cloud Texttospeech v1beta1 API
 
 .. automodule:: google.cloud.texttospeech_v1beta1.types
     :members:
+    :undoc-members:
+    :show-inheritance:
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/async_client.py b/google/cloud/texttospeech_v1/services/text_to_speech/async_client.py
index 3d94944e..6321e073 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/async_client.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/async_client.py
@@ -43,9 +43,72 @@ class TextToSpeechAsyncClient:
     DEFAULT_ENDPOINT = TextToSpeechClient.DEFAULT_ENDPOINT
     DEFAULT_MTLS_ENDPOINT = TextToSpeechClient.DEFAULT_MTLS_ENDPOINT
 
-    from_service_account_file = TextToSpeechClient.from_service_account_file
+    common_billing_account_path = staticmethod(
+        TextToSpeechClient.common_billing_account_path
+    )
+    parse_common_billing_account_path = staticmethod(
+        TextToSpeechClient.parse_common_billing_account_path
+    )
+
+    common_folder_path = staticmethod(TextToSpeechClient.common_folder_path)
+    parse_common_folder_path = staticmethod(TextToSpeechClient.parse_common_folder_path)
+
+    common_organization_path = staticmethod(TextToSpeechClient.common_organization_path)
+    parse_common_organization_path = staticmethod(
+        TextToSpeechClient.parse_common_organization_path
+    )
+
+    common_project_path = staticmethod(TextToSpeechClient.common_project_path)
+    parse_common_project_path = staticmethod(
+        TextToSpeechClient.parse_common_project_path
+    )
+
+    common_location_path = staticmethod(TextToSpeechClient.common_location_path)
+    parse_common_location_path = staticmethod(
+        TextToSpeechClient.parse_common_location_path
+    )
+
+    @classmethod
+    def from_service_account_info(cls, info: dict, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials info.
+
+        Args:
+            info (dict): The service account private key info.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechAsyncClient: The constructed client.
+        """
+        return TextToSpeechClient.from_service_account_info.__func__(TextToSpeechAsyncClient, info, *args, **kwargs)  # type: ignore
+
+    @classmethod
+    def from_service_account_file(cls, filename: str, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials
+        file.
+
+        Args:
+            filename (str): The path to the service account private key json
+                file.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechAsyncClient: The constructed client.
+        """
+        return TextToSpeechClient.from_service_account_file.__func__(TextToSpeechAsyncClient, filename, *args, **kwargs)  # type: ignore
+
     from_service_account_json = from_service_account_file
 
+    @property
+    def transport(self) -> TextToSpeechTransport:
+        """Return the transport used by the client instance.
+
+        Returns:
+            TextToSpeechTransport: The transport used by the client instance.
+        """
+        return self._client.transport
+
     get_transport_class = functools.partial(
         type(TextToSpeechClient).get_transport_class, type(TextToSpeechClient)
     )
@@ -72,16 +135,19 @@ def __init__(
             client_options (ClientOptions): Custom options for the client. It
                 won't take effect if a ``transport`` instance is provided.
                 (1) The ``api_endpoint`` property can be used to override the
-                default endpoint provided by the client. GOOGLE_API_USE_MTLS
+                default endpoint provided by the client. GOOGLE_API_USE_MTLS_ENDPOINT
                 environment variable can also be used to override the endpoint:
                 "always" (always use the default mTLS endpoint), "never" (always
-                use the default regular endpoint, this is the default value for
-                the environment variable) and "auto" (auto switch to the default
-                mTLS endpoint if client SSL credentials is present). However,
-                the ``api_endpoint`` property takes precedence if provided.
-                (2) The ``client_cert_source`` property is used to provide client
-                SSL credentials for mutual TLS transport. If not provided, the
-                default SSL credentials will be used if present.
+                use the default regular endpoint) and "auto" (auto switch to the
+                default mTLS endpoint if client certificate is present, this is
+                the default value). However, the ``api_endpoint`` property takes
+                precedence if provided.
+                (2) If GOOGLE_API_USE_CLIENT_CERTIFICATE environment variable
+                is "true", then the ``client_cert_source`` property can be used
+                to provide client certificate for mutual TLS transport. If
+                not provided, the default SSL client certificate will be used if
+                present. If GOOGLE_API_USE_CLIENT_CERTIFICATE is "false" or not
+                set, no client certificate will be used.
 
         Raises:
             google.auth.exceptions.MutualTlsChannelError: If mutual TLS transport
@@ -107,7 +173,7 @@ async def list_voices(
         r"""Returns a list of Voice supported for synthesis.
 
         Args:
-            request (:class:`~.cloud_tts.ListVoicesRequest`):
+            request (:class:`google.cloud.texttospeech_v1.types.ListVoicesRequest`):
                 The request object. The top-level message sent by the
                 client for the `ListVoices` method.
             language_code (:class:`str`):
@@ -121,6 +187,7 @@ async def list_voices(
                 (Norwegian Bokmal) voices; specifying "zh" will also get
                 supported "cmn-\*" voices; specifying "zh-hk" will also
                 get supported "yue-\*" voices.
+
                 This corresponds to the ``language_code`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -132,15 +199,16 @@ async def list_voices(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.ListVoicesResponse:
-                The message returned to the client by the ``ListVoices``
+            google.cloud.texttospeech_v1.types.ListVoicesResponse:
+                The message returned to the client by the ListVoices
                 method.
 
         """
         # Create or coerce a protobuf request object.
         # Sanity check: If we got a request object, we should *not* have
         # gotten any keyword arguments that map to the request.
-        if request is not None and any([language_code]):
+        has_flattened_params = any([language_code])
+        if request is not None and has_flattened_params:
             raise ValueError(
                 "If the `request` argument is set, then none of "
                 "the individual field arguments should be set."
@@ -158,7 +226,15 @@ async def list_voices(
         # and friendly error handling.
         rpc = gapic_v1.method_async.wrap_method(
             self._client._transport.list_voices,
-            default_timeout=None,
+            default_retry=retries.Retry(
+                initial=0.1,
+                maximum=60.0,
+                multiplier=1.3,
+                predicate=retries.if_exception_type(
+                    exceptions.DeadlineExceeded, exceptions.ServiceUnavailable,
+                ),
+            ),
+            default_timeout=600.0,
             client_info=DEFAULT_CLIENT_INFO,
         )
 
@@ -183,24 +259,27 @@ async def synthesize_speech(
         after all text input has been processed.
 
         Args:
-            request (:class:`~.cloud_tts.SynthesizeSpeechRequest`):
+            request (:class:`google.cloud.texttospeech_v1.types.SynthesizeSpeechRequest`):
                 The request object. The top-level message sent by the
                 client for the `SynthesizeSpeech` method.
-            input (:class:`~.cloud_tts.SynthesisInput`):
+            input (:class:`google.cloud.texttospeech_v1.types.SynthesisInput`):
                 Required. The Synthesizer requires
                 either plain text or SSML as input.
+
                 This corresponds to the ``input`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            voice (:class:`~.cloud_tts.VoiceSelectionParams`):
+            voice (:class:`google.cloud.texttospeech_v1.types.VoiceSelectionParams`):
                 Required. The desired voice of the
                 synthesized audio.
+
                 This corresponds to the ``voice`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            audio_config (:class:`~.cloud_tts.AudioConfig`):
+            audio_config (:class:`google.cloud.texttospeech_v1.types.AudioConfig`):
                 Required. The configuration of the
                 synthesized audio.
+
                 This corresponds to the ``audio_config`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -212,15 +291,16 @@ async def synthesize_speech(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.SynthesizeSpeechResponse:
+            google.cloud.texttospeech_v1.types.SynthesizeSpeechResponse:
                 The message returned to the client by the
-                ``SynthesizeSpeech`` method.
+                SynthesizeSpeech method.
 
         """
         # Create or coerce a protobuf request object.
         # Sanity check: If we got a request object, we should *not* have
         # gotten any keyword arguments that map to the request.
-        if request is not None and any([input, voice, audio_config]):
+        has_flattened_params = any([input, voice, audio_config])
+        if request is not None and has_flattened_params:
             raise ValueError(
                 "If the `request` argument is set, then none of "
                 "the individual field arguments should be set."
@@ -242,7 +322,15 @@ async def synthesize_speech(
         # and friendly error handling.
         rpc = gapic_v1.method_async.wrap_method(
             self._client._transport.synthesize_speech,
-            default_timeout=None,
+            default_retry=retries.Retry(
+                initial=0.1,
+                maximum=60.0,
+                multiplier=1.3,
+                predicate=retries.if_exception_type(
+                    exceptions.DeadlineExceeded, exceptions.ServiceUnavailable,
+                ),
+            ),
+            default_timeout=600.0,
             client_info=DEFAULT_CLIENT_INFO,
         )
 
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/client.py b/google/cloud/texttospeech_v1/services/text_to_speech/client.py
index c365b0fa..836ac5a3 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/client.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/client.py
@@ -16,17 +16,19 @@
 #
 
 from collections import OrderedDict
+from distutils import util
 import os
 import re
-from typing import Callable, Dict, Sequence, Tuple, Type, Union
+from typing import Callable, Dict, Optional, Sequence, Tuple, Type, Union
 import pkg_resources
 
-import google.api_core.client_options as ClientOptions  # type: ignore
+from google.api_core import client_options as client_options_lib  # type: ignore
 from google.api_core import exceptions  # type: ignore
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import retry as retries  # type: ignore
 from google.auth import credentials  # type: ignore
 from google.auth.transport import mtls  # type: ignore
+from google.auth.transport.grpc import SslCredentials  # type: ignore
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
@@ -105,6 +107,22 @@ def _get_default_mtls_endpoint(api_endpoint):
         DEFAULT_ENDPOINT
     )
 
+    @classmethod
+    def from_service_account_info(cls, info: dict, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials info.
+
+        Args:
+            info (dict): The service account private key info.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechClient: The constructed client.
+        """
+        credentials = service_account.Credentials.from_service_account_info(info)
+        kwargs["credentials"] = credentials
+        return cls(*args, **kwargs)
+
     @classmethod
     def from_service_account_file(cls, filename: str, *args, **kwargs):
         """Creates an instance of this client using the provided credentials
@@ -117,7 +135,7 @@ def from_service_account_file(cls, filename: str, *args, **kwargs):
             kwargs: Additional arguments to pass to the constructor.
 
         Returns:
-            {@api.name}: The constructed client.
+            TextToSpeechClient: The constructed client.
         """
         credentials = service_account.Credentials.from_service_account_file(filename)
         kwargs["credentials"] = credentials
@@ -125,12 +143,80 @@ def from_service_account_file(cls, filename: str, *args, **kwargs):
 
     from_service_account_json = from_service_account_file
 
+    @property
+    def transport(self) -> TextToSpeechTransport:
+        """Return the transport used by the client instance.
+
+        Returns:
+            TextToSpeechTransport: The transport used by the client instance.
+        """
+        return self._transport
+
+    @staticmethod
+    def common_billing_account_path(billing_account: str,) -> str:
+        """Return a fully-qualified billing_account string."""
+        return "billingAccounts/{billing_account}".format(
+            billing_account=billing_account,
+        )
+
+    @staticmethod
+    def parse_common_billing_account_path(path: str) -> Dict[str, str]:
+        """Parse a billing_account path into its component segments."""
+        m = re.match(r"^billingAccounts/(?P<billing_account>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_folder_path(folder: str,) -> str:
+        """Return a fully-qualified folder string."""
+        return "folders/{folder}".format(folder=folder,)
+
+    @staticmethod
+    def parse_common_folder_path(path: str) -> Dict[str, str]:
+        """Parse a folder path into its component segments."""
+        m = re.match(r"^folders/(?P<folder>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_organization_path(organization: str,) -> str:
+        """Return a fully-qualified organization string."""
+        return "organizations/{organization}".format(organization=organization,)
+
+    @staticmethod
+    def parse_common_organization_path(path: str) -> Dict[str, str]:
+        """Parse a organization path into its component segments."""
+        m = re.match(r"^organizations/(?P<organization>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_project_path(project: str,) -> str:
+        """Return a fully-qualified project string."""
+        return "projects/{project}".format(project=project,)
+
+    @staticmethod
+    def parse_common_project_path(path: str) -> Dict[str, str]:
+        """Parse a project path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_location_path(project: str, location: str,) -> str:
+        """Return a fully-qualified location string."""
+        return "projects/{project}/locations/{location}".format(
+            project=project, location=location,
+        )
+
+    @staticmethod
+    def parse_common_location_path(path: str) -> Dict[str, str]:
+        """Parse a location path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)/locations/(?P<location>.+?)$", path)
+        return m.groupdict() if m else {}
+
     def __init__(
         self,
         *,
-        credentials: credentials.Credentials = None,
-        transport: Union[str, TextToSpeechTransport] = None,
-        client_options: ClientOptions = None,
+        credentials: Optional[credentials.Credentials] = None,
+        transport: Union[str, TextToSpeechTransport, None] = None,
+        client_options: Optional[client_options_lib.ClientOptions] = None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
         """Instantiate the text to speech client.
@@ -141,26 +227,29 @@ def __init__(
                 credentials identify the application to the service; if none
                 are specified, the client will attempt to ascertain the
                 credentials from the environment.
-            transport (Union[str, ~.TextToSpeechTransport]): The
+            transport (Union[str, TextToSpeechTransport]): The
                 transport to use. If set to None, a transport is chosen
                 automatically.
-            client_options (ClientOptions): Custom options for the client. It
-                won't take effect if a ``transport`` instance is provided.
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. It won't take effect if a ``transport`` instance is provided.
                 (1) The ``api_endpoint`` property can be used to override the
-                default endpoint provided by the client. GOOGLE_API_USE_MTLS
+                default endpoint provided by the client. GOOGLE_API_USE_MTLS_ENDPOINT
                 environment variable can also be used to override the endpoint:
                 "always" (always use the default mTLS endpoint), "never" (always
-                use the default regular endpoint, this is the default value for
-                the environment variable) and "auto" (auto switch to the default
-                mTLS endpoint if client SSL credentials is present). However,
-                the ``api_endpoint`` property takes precedence if provided.
-                (2) The ``client_cert_source`` property is used to provide client
-                SSL credentials for mutual TLS transport. If not provided, the
-                default SSL credentials will be used if present.
-            client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
-                The client info used to send a user-agent string along with	
-                API requests. If ``None``, then default info will be used.	
-                Generally, you only need to set this if you're developing	
+                use the default regular endpoint) and "auto" (auto switch to the
+                default mTLS endpoint if client certificate is present, this is
+                the default value). However, the ``api_endpoint`` property takes
+                precedence if provided.
+                (2) If GOOGLE_API_USE_CLIENT_CERTIFICATE environment variable
+                is "true", then the ``client_cert_source`` property can be used
+                to provide client certificate for mutual TLS transport. If
+                not provided, the default SSL client certificate will be used if
+                present. If GOOGLE_API_USE_CLIENT_CERTIFICATE is "false" or not
+                set, no client certificate will be used.
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
                 your own client library.
 
         Raises:
@@ -168,29 +257,43 @@ def __init__(
                 creation failed for any reason.
         """
         if isinstance(client_options, dict):
-            client_options = ClientOptions.from_dict(client_options)
+            client_options = client_options_lib.from_dict(client_options)
         if client_options is None:
-            client_options = ClientOptions.ClientOptions()
+            client_options = client_options_lib.ClientOptions()
+
+        # Create SSL credentials for mutual TLS if needed.
+        use_client_cert = bool(
+            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
+        )
+
+        client_cert_source_func = None
+        is_mtls = False
+        if use_client_cert:
+            if client_options.client_cert_source:
+                is_mtls = True
+                client_cert_source_func = client_options.client_cert_source
+            else:
+                is_mtls = mtls.has_default_client_cert_source()
+                client_cert_source_func = (
+                    mtls.default_client_cert_source() if is_mtls else None
+                )
 
-        if client_options.api_endpoint is None:
-            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS", "never")
+        # Figure out which api endpoint to use.
+        if client_options.api_endpoint is not None:
+            api_endpoint = client_options.api_endpoint
+        else:
+            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
             if use_mtls_env == "never":
-                client_options.api_endpoint = self.DEFAULT_ENDPOINT
+                api_endpoint = self.DEFAULT_ENDPOINT
             elif use_mtls_env == "always":
-                client_options.api_endpoint = self.DEFAULT_MTLS_ENDPOINT
+                api_endpoint = self.DEFAULT_MTLS_ENDPOINT
             elif use_mtls_env == "auto":
-                has_client_cert_source = (
-                    client_options.client_cert_source is not None
-                    or mtls.has_default_client_cert_source()
-                )
-                client_options.api_endpoint = (
-                    self.DEFAULT_MTLS_ENDPOINT
-                    if has_client_cert_source
-                    else self.DEFAULT_ENDPOINT
+                api_endpoint = (
+                    self.DEFAULT_MTLS_ENDPOINT if is_mtls else self.DEFAULT_ENDPOINT
                 )
             else:
                 raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: never, auto, always"
+                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted values: never, auto, always"
                 )
 
         # Save or instantiate the transport.
@@ -214,10 +317,9 @@ def __init__(
             self._transport = Transport(
                 credentials=credentials,
                 credentials_file=client_options.credentials_file,
-                host=client_options.api_endpoint,
+                host=api_endpoint,
                 scopes=client_options.scopes,
-                api_mtls_endpoint=client_options.api_endpoint,
-                client_cert_source=client_options.client_cert_source,
+                client_cert_source_for_mtls=client_cert_source_func,
                 quota_project_id=client_options.quota_project_id,
                 client_info=client_info,
             )
@@ -234,10 +336,10 @@ def list_voices(
         r"""Returns a list of Voice supported for synthesis.
 
         Args:
-            request (:class:`~.cloud_tts.ListVoicesRequest`):
+            request (google.cloud.texttospeech_v1.types.ListVoicesRequest):
                 The request object. The top-level message sent by the
                 client for the `ListVoices` method.
-            language_code (:class:`str`):
+            language_code (str):
                 Optional. Recommended.
                 `BCP-47 <https://www.rfc-editor.org/rfc/bcp/bcp47.txt>`__
                 language tag. If specified, the ListVoices call will
@@ -248,6 +350,7 @@ def list_voices(
                 (Norwegian Bokmal) voices; specifying "zh" will also get
                 supported "cmn-\*" voices; specifying "zh-hk" will also
                 get supported "yue-\*" voices.
+
                 This corresponds to the ``language_code`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -259,8 +362,8 @@ def list_voices(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.ListVoicesResponse:
-                The message returned to the client by the ``ListVoices``
+            google.cloud.texttospeech_v1.types.ListVoicesResponse:
+                The message returned to the client by the ListVoices
                 method.
 
         """
@@ -312,24 +415,27 @@ def synthesize_speech(
         after all text input has been processed.
 
         Args:
-            request (:class:`~.cloud_tts.SynthesizeSpeechRequest`):
+            request (google.cloud.texttospeech_v1.types.SynthesizeSpeechRequest):
                 The request object. The top-level message sent by the
                 client for the `SynthesizeSpeech` method.
-            input (:class:`~.cloud_tts.SynthesisInput`):
+            input (google.cloud.texttospeech_v1.types.SynthesisInput):
                 Required. The Synthesizer requires
                 either plain text or SSML as input.
+
                 This corresponds to the ``input`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            voice (:class:`~.cloud_tts.VoiceSelectionParams`):
+            voice (google.cloud.texttospeech_v1.types.VoiceSelectionParams):
                 Required. The desired voice of the
                 synthesized audio.
+
                 This corresponds to the ``voice`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            audio_config (:class:`~.cloud_tts.AudioConfig`):
+            audio_config (google.cloud.texttospeech_v1.types.AudioConfig):
                 Required. The configuration of the
                 synthesized audio.
+
                 This corresponds to the ``audio_config`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -341,9 +447,9 @@ def synthesize_speech(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.SynthesizeSpeechResponse:
+            google.cloud.texttospeech_v1.types.SynthesizeSpeechResponse:
                 The message returned to the client by the
-                ``SynthesizeSpeech`` method.
+                SynthesizeSpeech method.
 
         """
         # Create or coerce a protobuf request object.
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/transports/__init__.py b/google/cloud/texttospeech_v1/services/text_to_speech/transports/__init__.py
index 3a92efc9..ce3b91f1 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/transports/__init__.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/transports/__init__.py
@@ -28,7 +28,6 @@
 _transport_registry["grpc"] = TextToSpeechGrpcTransport
 _transport_registry["grpc_asyncio"] = TextToSpeechGrpcAsyncIOTransport
 
-
 __all__ = (
     "TextToSpeechTransport",
     "TextToSpeechGrpcTransport",
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/transports/base.py b/google/cloud/texttospeech_v1/services/text_to_speech/transports/base.py
index d891cc63..9c27cc48 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/transports/base.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/transports/base.py
@@ -19,7 +19,7 @@
 import typing
 import pkg_resources
 
-from google import auth
+from google import auth  # type: ignore
 from google.api_core import exceptions  # type: ignore
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import retry as retries  # type: ignore
@@ -107,10 +107,30 @@ def _prep_wrapped_messages(self, client_info):
         # Precompute the wrapped methods.
         self._wrapped_methods = {
             self.list_voices: gapic_v1.method.wrap_method(
-                self.list_voices, default_timeout=None, client_info=client_info,
+                self.list_voices,
+                default_retry=retries.Retry(
+                    initial=0.1,
+                    maximum=60.0,
+                    multiplier=1.3,
+                    predicate=retries.if_exception_type(
+                        exceptions.DeadlineExceeded, exceptions.ServiceUnavailable,
+                    ),
+                ),
+                default_timeout=600.0,
+                client_info=client_info,
             ),
             self.synthesize_speech: gapic_v1.method.wrap_method(
-                self.synthesize_speech, default_timeout=None, client_info=client_info,
+                self.synthesize_speech,
+                default_retry=retries.Retry(
+                    initial=0.1,
+                    maximum=60.0,
+                    multiplier=1.3,
+                    predicate=retries.if_exception_type(
+                        exceptions.DeadlineExceeded, exceptions.ServiceUnavailable,
+                    ),
+                ),
+                default_timeout=600.0,
+                client_info=client_info,
             ),
         }
 
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc.py b/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc.py
index c44e247a..e31266e6 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 #
 
+import warnings
 from typing import Callable, Dict, Optional, Sequence, Tuple
 
 from google.api_core import grpc_helpers  # type: ignore
@@ -23,7 +24,6 @@
 from google.auth import credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 
-
 import grpc  # type: ignore
 
 from google.cloud.texttospeech_v1.types import cloud_tts
@@ -56,6 +56,8 @@ def __init__(
         channel: grpc.Channel = None,
         api_mtls_endpoint: str = None,
         client_cert_source: Callable[[], Tuple[bytes, bytes]] = None,
+        ssl_channel_credentials: grpc.ChannelCredentials = None,
+        client_cert_source_for_mtls: Callable[[], Tuple[bytes, bytes]] = None,
         quota_project_id: Optional[str] = None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
@@ -76,20 +78,26 @@ def __init__(
                 ignored if ``channel`` is provided.
             channel (Optional[grpc.Channel]): A ``Channel`` instance through
                 which to make calls.
-            api_mtls_endpoint (Optional[str]): The mutual TLS endpoint. If
-                provided, it overrides the ``host`` argument and tries to create
+            api_mtls_endpoint (Optional[str]): Deprecated. The mutual TLS endpoint.
+                If provided, it overrides the ``host`` argument and tries to create
                 a mutual TLS channel with client SSL credentials from
                 ``client_cert_source`` or applicatin default SSL credentials.
-            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]): A
-                callback to provide client SSL certificate bytes and private key
-                bytes, both in PEM format. It is ignored if ``api_mtls_endpoint``
-                is None.
+            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                Deprecated. A callback to provide client SSL certificate bytes and
+                private key bytes, both in PEM format. It is ignored if
+                ``api_mtls_endpoint`` is None.
+            ssl_channel_credentials (grpc.ChannelCredentials): SSL credentials
+                for grpc channel. It is ignored if ``channel`` is provided.
+            client_cert_source_for_mtls (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                A callback to provide client certificate bytes and private key bytes,
+                both in PEM format. It is used to configure mutual TLS channel. It is
+                ignored if ``channel`` or ``ssl_channel_credentials`` is provided.
             quota_project_id (Optional[str]): An optional project to use for billing
                 and quota.
-            client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
-                The client info used to send a user-agent string along with	
-                API requests. If ``None``, then default info will be used.	
-                Generally, you only need to set this if you're developing	
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
                 your own client library.
 
         Raises:
@@ -98,6 +106,13 @@ def __init__(
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
+        if api_mtls_endpoint:
+            warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
+        if client_cert_source:
+            warnings.warn("client_cert_source is deprecated", DeprecationWarning)
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
@@ -105,6 +120,7 @@ def __init__(
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             host = (
                 api_mtls_endpoint
@@ -135,6 +151,38 @@ def __init__(
                 ssl_credentials=ssl_credentials,
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            self._ssl_channel_credentials = ssl_credentials
+        else:
+            host = host if ":" in host else host + ":443"
+
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
+            if client_cert_source_for_mtls and not ssl_channel_credentials:
+                cert, key = client_cert_source_for_mtls()
+                self._ssl_channel_credentials = grpc.ssl_channel_credentials(
+                    certificate_chain=cert, private_key=key
+                )
+
+            # create a new channel. The provided one is ignored.
+            self._grpc_channel = type(self).create_channel(
+                host,
+                credentials=credentials,
+                credentials_file=credentials_file,
+                ssl_credentials=self._ssl_channel_credentials,
+                scopes=scopes or self.AUTH_SCOPES,
+                quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
             )
 
         self._stubs = {}  # type: Dict[str, Callable]
@@ -161,7 +209,7 @@ def create_channel(
     ) -> grpc.Channel:
         """Create and return a gRPC channel object.
         Args:
-            address (Optionsl[str]): The host for the channel to use.
+            address (Optional[str]): The host for the channel to use.
             credentials (Optional[~.Credentials]): The
                 authorization credentials to attach to requests. These
                 credentials identify this application to the service. If
@@ -196,19 +244,8 @@ def create_channel(
 
     @property
     def grpc_channel(self) -> grpc.Channel:
-        """Create the channel designed to connect to this service.
-
-        This property caches on the instance; repeated calls return
-        the same channel.
+        """Return the channel designed to connect to this service.
         """
-        # Sanity check: Only create a new channel if we do not already
-        # have one.
-        if not hasattr(self, "_grpc_channel"):
-            self._grpc_channel = self.create_channel(
-                self._host, credentials=self._credentials,
-            )
-
-        # Return the channel from cache.
         return self._grpc_channel
 
     @property
diff --git a/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc_asyncio.py b/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc_asyncio.py
index 4105e365..88dd60a1 100644
--- a/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc_asyncio.py
+++ b/google/cloud/texttospeech_v1/services/text_to_speech/transports/grpc_asyncio.py
@@ -15,10 +15,12 @@
 # limitations under the License.
 #
 
+import warnings
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Tuple
 
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import grpc_helpers_async  # type: ignore
+from google import auth  # type: ignore
 from google.auth import credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 
@@ -98,6 +100,8 @@ def __init__(
         channel: aio.Channel = None,
         api_mtls_endpoint: str = None,
         client_cert_source: Callable[[], Tuple[bytes, bytes]] = None,
+        ssl_channel_credentials: grpc.ChannelCredentials = None,
+        client_cert_source_for_mtls: Callable[[], Tuple[bytes, bytes]] = None,
         quota_project_id=None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
@@ -119,14 +123,20 @@ def __init__(
                 are passed to :func:`google.auth.default`.
             channel (Optional[aio.Channel]): A ``Channel`` instance through
                 which to make calls.
-            api_mtls_endpoint (Optional[str]): The mutual TLS endpoint. If
-                provided, it overrides the ``host`` argument and tries to create
+            api_mtls_endpoint (Optional[str]): Deprecated. The mutual TLS endpoint.
+                If provided, it overrides the ``host`` argument and tries to create
                 a mutual TLS channel with client SSL credentials from
                 ``client_cert_source`` or applicatin default SSL credentials.
-            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]): A
-                callback to provide client SSL certificate bytes and private key
-                bytes, both in PEM format. It is ignored if ``api_mtls_endpoint``
-                is None.
+            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                Deprecated. A callback to provide client SSL certificate bytes and
+                private key bytes, both in PEM format. It is ignored if
+                ``api_mtls_endpoint`` is None.
+            ssl_channel_credentials (grpc.ChannelCredentials): SSL credentials
+                for grpc channel. It is ignored if ``channel`` is provided.
+            client_cert_source_for_mtls (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                A callback to provide client certificate bytes and private key bytes,
+                both in PEM format. It is used to configure mutual TLS channel. It is
+                ignored if ``channel`` or ``ssl_channel_credentials`` is provided.
             quota_project_id (Optional[str]): An optional project to use for billing
                 and quota.
             client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
@@ -141,6 +151,13 @@ def __init__(
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
+        if api_mtls_endpoint:
+            warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
+        if client_cert_source:
+            warnings.warn("client_cert_source is deprecated", DeprecationWarning)
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
@@ -148,6 +165,7 @@ def __init__(
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             host = (
                 api_mtls_endpoint
@@ -155,6 +173,11 @@ def __init__(
                 else api_mtls_endpoint + ":443"
             )
 
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
             # Create SSL credentials with client_cert_source or application
             # default SSL credentials.
             if client_cert_source:
@@ -173,6 +196,38 @@ def __init__(
                 ssl_credentials=ssl_credentials,
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            self._ssl_channel_credentials = ssl_credentials
+        else:
+            host = host if ":" in host else host + ":443"
+
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
+            if client_cert_source_for_mtls and not ssl_channel_credentials:
+                cert, key = client_cert_source_for_mtls()
+                self._ssl_channel_credentials = grpc.ssl_channel_credentials(
+                    certificate_chain=cert, private_key=key
+                )
+
+            # create a new channel. The provided one is ignored.
+            self._grpc_channel = type(self).create_channel(
+                host,
+                credentials=credentials,
+                credentials_file=credentials_file,
+                ssl_credentials=self._ssl_channel_credentials,
+                scopes=scopes or self.AUTH_SCOPES,
+                quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
             )
 
         # Run the base constructor.
@@ -194,13 +249,6 @@ def grpc_channel(self) -> aio.Channel:
         This property caches on the instance; repeated calls return
         the same channel.
         """
-        # Sanity check: Only create a new channel if we do not already
-        # have one.
-        if not hasattr(self, "_grpc_channel"):
-            self._grpc_channel = self.create_channel(
-                self._host, credentials=self._credentials,
-            )
-
         # Return the channel from cache.
         return self._grpc_channel
 
diff --git a/google/cloud/texttospeech_v1/types/__init__.py b/google/cloud/texttospeech_v1/types/__init__.py
index 47b20ad9..d6e4a7af 100644
--- a/google/cloud/texttospeech_v1/types/__init__.py
+++ b/google/cloud/texttospeech_v1/types/__init__.py
@@ -16,24 +16,27 @@
 #
 
 from .cloud_tts import (
+    AudioConfig,
     ListVoicesRequest,
     ListVoicesResponse,
-    Voice,
-    SynthesizeSpeechRequest,
     SynthesisInput,
-    VoiceSelectionParams,
-    AudioConfig,
+    SynthesizeSpeechRequest,
     SynthesizeSpeechResponse,
+    Voice,
+    VoiceSelectionParams,
+    AudioEncoding,
+    SsmlVoiceGender,
 )
 
-
 __all__ = (
+    "AudioConfig",
     "ListVoicesRequest",
     "ListVoicesResponse",
-    "Voice",
-    "SynthesizeSpeechRequest",
     "SynthesisInput",
-    "VoiceSelectionParams",
-    "AudioConfig",
+    "SynthesizeSpeechRequest",
     "SynthesizeSpeechResponse",
+    "Voice",
+    "VoiceSelectionParams",
+    "AudioEncoding",
+    "SsmlVoiceGender",
 )
diff --git a/google/cloud/texttospeech_v1/types/cloud_tts.py b/google/cloud/texttospeech_v1/types/cloud_tts.py
index 602ffa03..c20d55df 100644
--- a/google/cloud/texttospeech_v1/types/cloud_tts.py
+++ b/google/cloud/texttospeech_v1/types/cloud_tts.py
@@ -80,7 +80,7 @@ class ListVoicesResponse(proto.Message):
     r"""The message returned to the client by the ``ListVoices`` method.
 
     Attributes:
-        voices (Sequence[~.cloud_tts.Voice]):
+        voices (Sequence[google.cloud.texttospeech_v1.types.Voice]):
             The list of voices.
     """
 
@@ -98,7 +98,7 @@ class Voice(proto.Message):
         name (str):
             The name of this voice.  Each distinct voice
             has a unique name.
-        ssml_gender (~.cloud_tts.SsmlVoiceGender):
+        ssml_gender (google.cloud.texttospeech_v1.types.SsmlVoiceGender):
             The gender of this voice.
         natural_sample_rate_hertz (int):
             The natural sample rate (in hertz) for this
@@ -119,13 +119,13 @@ class SynthesizeSpeechRequest(proto.Message):
     ``SynthesizeSpeech`` method.
 
     Attributes:
-        input (~.cloud_tts.SynthesisInput):
+        input (google.cloud.texttospeech_v1.types.SynthesisInput):
             Required. The Synthesizer requires either
             plain text or SSML as input.
-        voice (~.cloud_tts.VoiceSelectionParams):
+        voice (google.cloud.texttospeech_v1.types.VoiceSelectionParams):
             Required. The desired voice of the
             synthesized audio.
-        audio_config (~.cloud_tts.AudioConfig):
+        audio_config (google.cloud.texttospeech_v1.types.AudioConfig):
             Required. The configuration of the
             synthesized audio.
     """
@@ -182,7 +182,7 @@ class VoiceSelectionParams(proto.Message):
             The name of the voice. If not set, the service will choose a
             voice based on the other parameters such as language_code
             and gender.
-        ssml_gender (~.cloud_tts.SsmlVoiceGender):
+        ssml_gender (google.cloud.texttospeech_v1.types.SsmlVoiceGender):
             The preferred gender of the voice. If not set, the service
             will choose a voice based on the other parameters such as
             language_code and name. Note that this is only a preference,
@@ -202,7 +202,7 @@ class AudioConfig(proto.Message):
     r"""Description of audio data to be synthesized.
 
     Attributes:
-        audio_encoding (~.cloud_tts.AudioEncoding):
+        audio_encoding (google.cloud.texttospeech_v1.types.AudioEncoding):
             Required. The format of the audio byte
             stream.
         speaking_rate (float):
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/async_client.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/async_client.py
index 4957ceda..b505fbbc 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/async_client.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/async_client.py
@@ -43,9 +43,72 @@ class TextToSpeechAsyncClient:
     DEFAULT_ENDPOINT = TextToSpeechClient.DEFAULT_ENDPOINT
     DEFAULT_MTLS_ENDPOINT = TextToSpeechClient.DEFAULT_MTLS_ENDPOINT
 
-    from_service_account_file = TextToSpeechClient.from_service_account_file
+    common_billing_account_path = staticmethod(
+        TextToSpeechClient.common_billing_account_path
+    )
+    parse_common_billing_account_path = staticmethod(
+        TextToSpeechClient.parse_common_billing_account_path
+    )
+
+    common_folder_path = staticmethod(TextToSpeechClient.common_folder_path)
+    parse_common_folder_path = staticmethod(TextToSpeechClient.parse_common_folder_path)
+
+    common_organization_path = staticmethod(TextToSpeechClient.common_organization_path)
+    parse_common_organization_path = staticmethod(
+        TextToSpeechClient.parse_common_organization_path
+    )
+
+    common_project_path = staticmethod(TextToSpeechClient.common_project_path)
+    parse_common_project_path = staticmethod(
+        TextToSpeechClient.parse_common_project_path
+    )
+
+    common_location_path = staticmethod(TextToSpeechClient.common_location_path)
+    parse_common_location_path = staticmethod(
+        TextToSpeechClient.parse_common_location_path
+    )
+
+    @classmethod
+    def from_service_account_info(cls, info: dict, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials info.
+
+        Args:
+            info (dict): The service account private key info.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechAsyncClient: The constructed client.
+        """
+        return TextToSpeechClient.from_service_account_info.__func__(TextToSpeechAsyncClient, info, *args, **kwargs)  # type: ignore
+
+    @classmethod
+    def from_service_account_file(cls, filename: str, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials
+        file.
+
+        Args:
+            filename (str): The path to the service account private key json
+                file.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechAsyncClient: The constructed client.
+        """
+        return TextToSpeechClient.from_service_account_file.__func__(TextToSpeechAsyncClient, filename, *args, **kwargs)  # type: ignore
+
     from_service_account_json = from_service_account_file
 
+    @property
+    def transport(self) -> TextToSpeechTransport:
+        """Return the transport used by the client instance.
+
+        Returns:
+            TextToSpeechTransport: The transport used by the client instance.
+        """
+        return self._client.transport
+
     get_transport_class = functools.partial(
         type(TextToSpeechClient).get_transport_class, type(TextToSpeechClient)
     )
@@ -72,16 +135,19 @@ def __init__(
             client_options (ClientOptions): Custom options for the client. It
                 won't take effect if a ``transport`` instance is provided.
                 (1) The ``api_endpoint`` property can be used to override the
-                default endpoint provided by the client. GOOGLE_API_USE_MTLS
+                default endpoint provided by the client. GOOGLE_API_USE_MTLS_ENDPOINT
                 environment variable can also be used to override the endpoint:
                 "always" (always use the default mTLS endpoint), "never" (always
-                use the default regular endpoint, this is the default value for
-                the environment variable) and "auto" (auto switch to the default
-                mTLS endpoint if client SSL credentials is present). However,
-                the ``api_endpoint`` property takes precedence if provided.
-                (2) The ``client_cert_source`` property is used to provide client
-                SSL credentials for mutual TLS transport. If not provided, the
-                default SSL credentials will be used if present.
+                use the default regular endpoint) and "auto" (auto switch to the
+                default mTLS endpoint if client certificate is present, this is
+                the default value). However, the ``api_endpoint`` property takes
+                precedence if provided.
+                (2) If GOOGLE_API_USE_CLIENT_CERTIFICATE environment variable
+                is "true", then the ``client_cert_source`` property can be used
+                to provide client certificate for mutual TLS transport. If
+                not provided, the default SSL client certificate will be used if
+                present. If GOOGLE_API_USE_CLIENT_CERTIFICATE is "false" or not
+                set, no client certificate will be used.
 
         Raises:
             google.auth.exceptions.MutualTlsChannelError: If mutual TLS transport
@@ -107,7 +173,7 @@ async def list_voices(
         r"""Returns a list of Voice supported for synthesis.
 
         Args:
-            request (:class:`~.cloud_tts.ListVoicesRequest`):
+            request (:class:`google.cloud.texttospeech_v1beta1.types.ListVoicesRequest`):
                 The request object. The top-level message sent by the
                 client for the `ListVoices` method.
             language_code (:class:`str`):
@@ -121,6 +187,7 @@ async def list_voices(
                 (Norwegian Bokmal) voices; specifying "zh" will also get
                 supported "cmn-\*" voices; specifying "zh-hk" will also
                 get supported "yue-\*" voices.
+
                 This corresponds to the ``language_code`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -132,15 +199,16 @@ async def list_voices(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.ListVoicesResponse:
-                The message returned to the client by the ``ListVoices``
+            google.cloud.texttospeech_v1beta1.types.ListVoicesResponse:
+                The message returned to the client by the ListVoices
                 method.
 
         """
         # Create or coerce a protobuf request object.
         # Sanity check: If we got a request object, we should *not* have
         # gotten any keyword arguments that map to the request.
-        if request is not None and any([language_code]):
+        has_flattened_params = any([language_code])
+        if request is not None and has_flattened_params:
             raise ValueError(
                 "If the `request` argument is set, then none of "
                 "the individual field arguments should be set."
@@ -183,24 +251,27 @@ async def synthesize_speech(
         after all text input has been processed.
 
         Args:
-            request (:class:`~.cloud_tts.SynthesizeSpeechRequest`):
+            request (:class:`google.cloud.texttospeech_v1beta1.types.SynthesizeSpeechRequest`):
                 The request object. The top-level message sent by the
                 client for the `SynthesizeSpeech` method.
-            input (:class:`~.cloud_tts.SynthesisInput`):
+            input (:class:`google.cloud.texttospeech_v1beta1.types.SynthesisInput`):
                 Required. The Synthesizer requires
                 either plain text or SSML as input.
+
                 This corresponds to the ``input`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            voice (:class:`~.cloud_tts.VoiceSelectionParams`):
+            voice (:class:`google.cloud.texttospeech_v1beta1.types.VoiceSelectionParams`):
                 Required. The desired voice of the
                 synthesized audio.
+
                 This corresponds to the ``voice`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            audio_config (:class:`~.cloud_tts.AudioConfig`):
+            audio_config (:class:`google.cloud.texttospeech_v1beta1.types.AudioConfig`):
                 Required. The configuration of the
                 synthesized audio.
+
                 This corresponds to the ``audio_config`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -212,15 +283,16 @@ async def synthesize_speech(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.SynthesizeSpeechResponse:
+            google.cloud.texttospeech_v1beta1.types.SynthesizeSpeechResponse:
                 The message returned to the client by the
-                ``SynthesizeSpeech`` method.
+                SynthesizeSpeech method.
 
         """
         # Create or coerce a protobuf request object.
         # Sanity check: If we got a request object, we should *not* have
         # gotten any keyword arguments that map to the request.
-        if request is not None and any([input, voice, audio_config]):
+        has_flattened_params = any([input, voice, audio_config])
+        if request is not None and has_flattened_params:
             raise ValueError(
                 "If the `request` argument is set, then none of "
                 "the individual field arguments should be set."
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/client.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/client.py
index 2fa7e4ae..4f3f6a40 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/client.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/client.py
@@ -16,17 +16,19 @@
 #
 
 from collections import OrderedDict
+from distutils import util
 import os
 import re
-from typing import Callable, Dict, Sequence, Tuple, Type, Union
+from typing import Callable, Dict, Optional, Sequence, Tuple, Type, Union
 import pkg_resources
 
-import google.api_core.client_options as ClientOptions  # type: ignore
+from google.api_core import client_options as client_options_lib  # type: ignore
 from google.api_core import exceptions  # type: ignore
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import retry as retries  # type: ignore
 from google.auth import credentials  # type: ignore
 from google.auth.transport import mtls  # type: ignore
+from google.auth.transport.grpc import SslCredentials  # type: ignore
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
@@ -105,6 +107,22 @@ def _get_default_mtls_endpoint(api_endpoint):
         DEFAULT_ENDPOINT
     )
 
+    @classmethod
+    def from_service_account_info(cls, info: dict, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials info.
+
+        Args:
+            info (dict): The service account private key info.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            TextToSpeechClient: The constructed client.
+        """
+        credentials = service_account.Credentials.from_service_account_info(info)
+        kwargs["credentials"] = credentials
+        return cls(*args, **kwargs)
+
     @classmethod
     def from_service_account_file(cls, filename: str, *args, **kwargs):
         """Creates an instance of this client using the provided credentials
@@ -117,7 +135,7 @@ def from_service_account_file(cls, filename: str, *args, **kwargs):
             kwargs: Additional arguments to pass to the constructor.
 
         Returns:
-            {@api.name}: The constructed client.
+            TextToSpeechClient: The constructed client.
         """
         credentials = service_account.Credentials.from_service_account_file(filename)
         kwargs["credentials"] = credentials
@@ -125,12 +143,80 @@ def from_service_account_file(cls, filename: str, *args, **kwargs):
 
     from_service_account_json = from_service_account_file
 
+    @property
+    def transport(self) -> TextToSpeechTransport:
+        """Return the transport used by the client instance.
+
+        Returns:
+            TextToSpeechTransport: The transport used by the client instance.
+        """
+        return self._transport
+
+    @staticmethod
+    def common_billing_account_path(billing_account: str,) -> str:
+        """Return a fully-qualified billing_account string."""
+        return "billingAccounts/{billing_account}".format(
+            billing_account=billing_account,
+        )
+
+    @staticmethod
+    def parse_common_billing_account_path(path: str) -> Dict[str, str]:
+        """Parse a billing_account path into its component segments."""
+        m = re.match(r"^billingAccounts/(?P<billing_account>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_folder_path(folder: str,) -> str:
+        """Return a fully-qualified folder string."""
+        return "folders/{folder}".format(folder=folder,)
+
+    @staticmethod
+    def parse_common_folder_path(path: str) -> Dict[str, str]:
+        """Parse a folder path into its component segments."""
+        m = re.match(r"^folders/(?P<folder>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_organization_path(organization: str,) -> str:
+        """Return a fully-qualified organization string."""
+        return "organizations/{organization}".format(organization=organization,)
+
+    @staticmethod
+    def parse_common_organization_path(path: str) -> Dict[str, str]:
+        """Parse a organization path into its component segments."""
+        m = re.match(r"^organizations/(?P<organization>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_project_path(project: str,) -> str:
+        """Return a fully-qualified project string."""
+        return "projects/{project}".format(project=project,)
+
+    @staticmethod
+    def parse_common_project_path(path: str) -> Dict[str, str]:
+        """Parse a project path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_location_path(project: str, location: str,) -> str:
+        """Return a fully-qualified location string."""
+        return "projects/{project}/locations/{location}".format(
+            project=project, location=location,
+        )
+
+    @staticmethod
+    def parse_common_location_path(path: str) -> Dict[str, str]:
+        """Parse a location path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)/locations/(?P<location>.+?)$", path)
+        return m.groupdict() if m else {}
+
     def __init__(
         self,
         *,
-        credentials: credentials.Credentials = None,
-        transport: Union[str, TextToSpeechTransport] = None,
-        client_options: ClientOptions = None,
+        credentials: Optional[credentials.Credentials] = None,
+        transport: Union[str, TextToSpeechTransport, None] = None,
+        client_options: Optional[client_options_lib.ClientOptions] = None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
         """Instantiate the text to speech client.
@@ -141,26 +227,29 @@ def __init__(
                 credentials identify the application to the service; if none
                 are specified, the client will attempt to ascertain the
                 credentials from the environment.
-            transport (Union[str, ~.TextToSpeechTransport]): The
+            transport (Union[str, TextToSpeechTransport]): The
                 transport to use. If set to None, a transport is chosen
                 automatically.
-            client_options (ClientOptions): Custom options for the client. It
-                won't take effect if a ``transport`` instance is provided.
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. It won't take effect if a ``transport`` instance is provided.
                 (1) The ``api_endpoint`` property can be used to override the
-                default endpoint provided by the client. GOOGLE_API_USE_MTLS
+                default endpoint provided by the client. GOOGLE_API_USE_MTLS_ENDPOINT
                 environment variable can also be used to override the endpoint:
                 "always" (always use the default mTLS endpoint), "never" (always
-                use the default regular endpoint, this is the default value for
-                the environment variable) and "auto" (auto switch to the default
-                mTLS endpoint if client SSL credentials is present). However,
-                the ``api_endpoint`` property takes precedence if provided.
-                (2) The ``client_cert_source`` property is used to provide client
-                SSL credentials for mutual TLS transport. If not provided, the
-                default SSL credentials will be used if present.
-            client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
-                The client info used to send a user-agent string along with	
-                API requests. If ``None``, then default info will be used.	
-                Generally, you only need to set this if you're developing	
+                use the default regular endpoint) and "auto" (auto switch to the
+                default mTLS endpoint if client certificate is present, this is
+                the default value). However, the ``api_endpoint`` property takes
+                precedence if provided.
+                (2) If GOOGLE_API_USE_CLIENT_CERTIFICATE environment variable
+                is "true", then the ``client_cert_source`` property can be used
+                to provide client certificate for mutual TLS transport. If
+                not provided, the default SSL client certificate will be used if
+                present. If GOOGLE_API_USE_CLIENT_CERTIFICATE is "false" or not
+                set, no client certificate will be used.
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
                 your own client library.
 
         Raises:
@@ -168,29 +257,43 @@ def __init__(
                 creation failed for any reason.
         """
         if isinstance(client_options, dict):
-            client_options = ClientOptions.from_dict(client_options)
+            client_options = client_options_lib.from_dict(client_options)
         if client_options is None:
-            client_options = ClientOptions.ClientOptions()
+            client_options = client_options_lib.ClientOptions()
+
+        # Create SSL credentials for mutual TLS if needed.
+        use_client_cert = bool(
+            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
+        )
+
+        client_cert_source_func = None
+        is_mtls = False
+        if use_client_cert:
+            if client_options.client_cert_source:
+                is_mtls = True
+                client_cert_source_func = client_options.client_cert_source
+            else:
+                is_mtls = mtls.has_default_client_cert_source()
+                client_cert_source_func = (
+                    mtls.default_client_cert_source() if is_mtls else None
+                )
 
-        if client_options.api_endpoint is None:
-            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS", "never")
+        # Figure out which api endpoint to use.
+        if client_options.api_endpoint is not None:
+            api_endpoint = client_options.api_endpoint
+        else:
+            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
             if use_mtls_env == "never":
-                client_options.api_endpoint = self.DEFAULT_ENDPOINT
+                api_endpoint = self.DEFAULT_ENDPOINT
             elif use_mtls_env == "always":
-                client_options.api_endpoint = self.DEFAULT_MTLS_ENDPOINT
+                api_endpoint = self.DEFAULT_MTLS_ENDPOINT
             elif use_mtls_env == "auto":
-                has_client_cert_source = (
-                    client_options.client_cert_source is not None
-                    or mtls.has_default_client_cert_source()
-                )
-                client_options.api_endpoint = (
-                    self.DEFAULT_MTLS_ENDPOINT
-                    if has_client_cert_source
-                    else self.DEFAULT_ENDPOINT
+                api_endpoint = (
+                    self.DEFAULT_MTLS_ENDPOINT if is_mtls else self.DEFAULT_ENDPOINT
                 )
             else:
                 raise MutualTLSChannelError(
-                    "Unsupported GOOGLE_API_USE_MTLS value. Accepted values: never, auto, always"
+                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted values: never, auto, always"
                 )
 
         # Save or instantiate the transport.
@@ -214,10 +317,9 @@ def __init__(
             self._transport = Transport(
                 credentials=credentials,
                 credentials_file=client_options.credentials_file,
-                host=client_options.api_endpoint,
+                host=api_endpoint,
                 scopes=client_options.scopes,
-                api_mtls_endpoint=client_options.api_endpoint,
-                client_cert_source=client_options.client_cert_source,
+                client_cert_source_for_mtls=client_cert_source_func,
                 quota_project_id=client_options.quota_project_id,
                 client_info=client_info,
             )
@@ -234,10 +336,10 @@ def list_voices(
         r"""Returns a list of Voice supported for synthesis.
 
         Args:
-            request (:class:`~.cloud_tts.ListVoicesRequest`):
+            request (google.cloud.texttospeech_v1beta1.types.ListVoicesRequest):
                 The request object. The top-level message sent by the
                 client for the `ListVoices` method.
-            language_code (:class:`str`):
+            language_code (str):
                 Optional. Recommended.
                 `BCP-47 <https://www.rfc-editor.org/rfc/bcp/bcp47.txt>`__
                 language tag. If specified, the ListVoices call will
@@ -248,6 +350,7 @@ def list_voices(
                 (Norwegian Bokmal) voices; specifying "zh" will also get
                 supported "cmn-\*" voices; specifying "zh-hk" will also
                 get supported "yue-\*" voices.
+
                 This corresponds to the ``language_code`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -259,8 +362,8 @@ def list_voices(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.ListVoicesResponse:
-                The message returned to the client by the ``ListVoices``
+            google.cloud.texttospeech_v1beta1.types.ListVoicesResponse:
+                The message returned to the client by the ListVoices
                 method.
 
         """
@@ -312,24 +415,27 @@ def synthesize_speech(
         after all text input has been processed.
 
         Args:
-            request (:class:`~.cloud_tts.SynthesizeSpeechRequest`):
+            request (google.cloud.texttospeech_v1beta1.types.SynthesizeSpeechRequest):
                 The request object. The top-level message sent by the
                 client for the `SynthesizeSpeech` method.
-            input (:class:`~.cloud_tts.SynthesisInput`):
+            input (google.cloud.texttospeech_v1beta1.types.SynthesisInput):
                 Required. The Synthesizer requires
                 either plain text or SSML as input.
+
                 This corresponds to the ``input`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            voice (:class:`~.cloud_tts.VoiceSelectionParams`):
+            voice (google.cloud.texttospeech_v1beta1.types.VoiceSelectionParams):
                 Required. The desired voice of the
                 synthesized audio.
+
                 This corresponds to the ``voice`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
-            audio_config (:class:`~.cloud_tts.AudioConfig`):
+            audio_config (google.cloud.texttospeech_v1beta1.types.AudioConfig):
                 Required. The configuration of the
                 synthesized audio.
+
                 This corresponds to the ``audio_config`` field
                 on the ``request`` instance; if ``request`` is provided, this
                 should not be set.
@@ -341,9 +447,9 @@ def synthesize_speech(
                 sent along with the request as metadata.
 
         Returns:
-            ~.cloud_tts.SynthesizeSpeechResponse:
+            google.cloud.texttospeech_v1beta1.types.SynthesizeSpeechResponse:
                 The message returned to the client by the
-                ``SynthesizeSpeech`` method.
+                SynthesizeSpeech method.
 
         """
         # Create or coerce a protobuf request object.
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/__init__.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/__init__.py
index 3a92efc9..ce3b91f1 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/__init__.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/__init__.py
@@ -28,7 +28,6 @@
 _transport_registry["grpc"] = TextToSpeechGrpcTransport
 _transport_registry["grpc_asyncio"] = TextToSpeechGrpcAsyncIOTransport
 
-
 __all__ = (
     "TextToSpeechTransport",
     "TextToSpeechGrpcTransport",
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/base.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/base.py
index dfd1be01..cdce4625 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/base.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/base.py
@@ -19,7 +19,7 @@
 import typing
 import pkg_resources
 
-from google import auth
+from google import auth  # type: ignore
 from google.api_core import exceptions  # type: ignore
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import retry as retries  # type: ignore
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc.py
index 95f453f6..9516ba39 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc.py
@@ -15,6 +15,7 @@
 # limitations under the License.
 #
 
+import warnings
 from typing import Callable, Dict, Optional, Sequence, Tuple
 
 from google.api_core import grpc_helpers  # type: ignore
@@ -23,7 +24,6 @@
 from google.auth import credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 
-
 import grpc  # type: ignore
 
 from google.cloud.texttospeech_v1beta1.types import cloud_tts
@@ -56,6 +56,8 @@ def __init__(
         channel: grpc.Channel = None,
         api_mtls_endpoint: str = None,
         client_cert_source: Callable[[], Tuple[bytes, bytes]] = None,
+        ssl_channel_credentials: grpc.ChannelCredentials = None,
+        client_cert_source_for_mtls: Callable[[], Tuple[bytes, bytes]] = None,
         quota_project_id: Optional[str] = None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
@@ -76,20 +78,26 @@ def __init__(
                 ignored if ``channel`` is provided.
             channel (Optional[grpc.Channel]): A ``Channel`` instance through
                 which to make calls.
-            api_mtls_endpoint (Optional[str]): The mutual TLS endpoint. If
-                provided, it overrides the ``host`` argument and tries to create
+            api_mtls_endpoint (Optional[str]): Deprecated. The mutual TLS endpoint.
+                If provided, it overrides the ``host`` argument and tries to create
                 a mutual TLS channel with client SSL credentials from
                 ``client_cert_source`` or applicatin default SSL credentials.
-            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]): A
-                callback to provide client SSL certificate bytes and private key
-                bytes, both in PEM format. It is ignored if ``api_mtls_endpoint``
-                is None.
+            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                Deprecated. A callback to provide client SSL certificate bytes and
+                private key bytes, both in PEM format. It is ignored if
+                ``api_mtls_endpoint`` is None.
+            ssl_channel_credentials (grpc.ChannelCredentials): SSL credentials
+                for grpc channel. It is ignored if ``channel`` is provided.
+            client_cert_source_for_mtls (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                A callback to provide client certificate bytes and private key bytes,
+                both in PEM format. It is used to configure mutual TLS channel. It is
+                ignored if ``channel`` or ``ssl_channel_credentials`` is provided.
             quota_project_id (Optional[str]): An optional project to use for billing
                 and quota.
-            client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
-                The client info used to send a user-agent string along with	
-                API requests. If ``None``, then default info will be used.	
-                Generally, you only need to set this if you're developing	
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
                 your own client library.
 
         Raises:
@@ -98,6 +106,13 @@ def __init__(
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
+        if api_mtls_endpoint:
+            warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
+        if client_cert_source:
+            warnings.warn("client_cert_source is deprecated", DeprecationWarning)
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
@@ -105,6 +120,7 @@ def __init__(
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             host = (
                 api_mtls_endpoint
@@ -135,6 +151,38 @@ def __init__(
                 ssl_credentials=ssl_credentials,
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            self._ssl_channel_credentials = ssl_credentials
+        else:
+            host = host if ":" in host else host + ":443"
+
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
+            if client_cert_source_for_mtls and not ssl_channel_credentials:
+                cert, key = client_cert_source_for_mtls()
+                self._ssl_channel_credentials = grpc.ssl_channel_credentials(
+                    certificate_chain=cert, private_key=key
+                )
+
+            # create a new channel. The provided one is ignored.
+            self._grpc_channel = type(self).create_channel(
+                host,
+                credentials=credentials,
+                credentials_file=credentials_file,
+                ssl_credentials=self._ssl_channel_credentials,
+                scopes=scopes or self.AUTH_SCOPES,
+                quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
             )
 
         self._stubs = {}  # type: Dict[str, Callable]
@@ -161,7 +209,7 @@ def create_channel(
     ) -> grpc.Channel:
         """Create and return a gRPC channel object.
         Args:
-            address (Optionsl[str]): The host for the channel to use.
+            address (Optional[str]): The host for the channel to use.
             credentials (Optional[~.Credentials]): The
                 authorization credentials to attach to requests. These
                 credentials identify this application to the service. If
@@ -196,19 +244,8 @@ def create_channel(
 
     @property
     def grpc_channel(self) -> grpc.Channel:
-        """Create the channel designed to connect to this service.
-
-        This property caches on the instance; repeated calls return
-        the same channel.
+        """Return the channel designed to connect to this service.
         """
-        # Sanity check: Only create a new channel if we do not already
-        # have one.
-        if not hasattr(self, "_grpc_channel"):
-            self._grpc_channel = self.create_channel(
-                self._host, credentials=self._credentials,
-            )
-
-        # Return the channel from cache.
         return self._grpc_channel
 
     @property
diff --git a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc_asyncio.py b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc_asyncio.py
index d2d77873..b36c4282 100644
--- a/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc_asyncio.py
+++ b/google/cloud/texttospeech_v1beta1/services/text_to_speech/transports/grpc_asyncio.py
@@ -15,10 +15,12 @@
 # limitations under the License.
 #
 
+import warnings
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Tuple
 
 from google.api_core import gapic_v1  # type: ignore
 from google.api_core import grpc_helpers_async  # type: ignore
+from google import auth  # type: ignore
 from google.auth import credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 
@@ -98,6 +100,8 @@ def __init__(
         channel: aio.Channel = None,
         api_mtls_endpoint: str = None,
         client_cert_source: Callable[[], Tuple[bytes, bytes]] = None,
+        ssl_channel_credentials: grpc.ChannelCredentials = None,
+        client_cert_source_for_mtls: Callable[[], Tuple[bytes, bytes]] = None,
         quota_project_id=None,
         client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
     ) -> None:
@@ -119,14 +123,20 @@ def __init__(
                 are passed to :func:`google.auth.default`.
             channel (Optional[aio.Channel]): A ``Channel`` instance through
                 which to make calls.
-            api_mtls_endpoint (Optional[str]): The mutual TLS endpoint. If
-                provided, it overrides the ``host`` argument and tries to create
+            api_mtls_endpoint (Optional[str]): Deprecated. The mutual TLS endpoint.
+                If provided, it overrides the ``host`` argument and tries to create
                 a mutual TLS channel with client SSL credentials from
                 ``client_cert_source`` or applicatin default SSL credentials.
-            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]): A
-                callback to provide client SSL certificate bytes and private key
-                bytes, both in PEM format. It is ignored if ``api_mtls_endpoint``
-                is None.
+            client_cert_source (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                Deprecated. A callback to provide client SSL certificate bytes and
+                private key bytes, both in PEM format. It is ignored if
+                ``api_mtls_endpoint`` is None.
+            ssl_channel_credentials (grpc.ChannelCredentials): SSL credentials
+                for grpc channel. It is ignored if ``channel`` is provided.
+            client_cert_source_for_mtls (Optional[Callable[[], Tuple[bytes, bytes]]]):
+                A callback to provide client certificate bytes and private key bytes,
+                both in PEM format. It is used to configure mutual TLS channel. It is
+                ignored if ``channel`` or ``ssl_channel_credentials`` is provided.
             quota_project_id (Optional[str]): An optional project to use for billing
                 and quota.
             client_info (google.api_core.gapic_v1.client_info.ClientInfo):	
@@ -141,6 +151,13 @@ def __init__(
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
+        if api_mtls_endpoint:
+            warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
+        if client_cert_source:
+            warnings.warn("client_cert_source is deprecated", DeprecationWarning)
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
@@ -148,6 +165,7 @@ def __init__(
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             host = (
                 api_mtls_endpoint
@@ -155,6 +173,11 @@ def __init__(
                 else api_mtls_endpoint + ":443"
             )
 
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
             # Create SSL credentials with client_cert_source or application
             # default SSL credentials.
             if client_cert_source:
@@ -173,6 +196,38 @@ def __init__(
                 ssl_credentials=ssl_credentials,
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            self._ssl_channel_credentials = ssl_credentials
+        else:
+            host = host if ":" in host else host + ":443"
+
+            if credentials is None:
+                credentials, _ = auth.default(
+                    scopes=self.AUTH_SCOPES, quota_project_id=quota_project_id
+                )
+
+            if client_cert_source_for_mtls and not ssl_channel_credentials:
+                cert, key = client_cert_source_for_mtls()
+                self._ssl_channel_credentials = grpc.ssl_channel_credentials(
+                    certificate_chain=cert, private_key=key
+                )
+
+            # create a new channel. The provided one is ignored.
+            self._grpc_channel = type(self).create_channel(
+                host,
+                credentials=credentials,
+                credentials_file=credentials_file,
+                ssl_credentials=self._ssl_channel_credentials,
+                scopes=scopes or self.AUTH_SCOPES,
+                quota_project_id=quota_project_id,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
             )
 
         # Run the base constructor.
@@ -194,13 +249,6 @@ def grpc_channel(self) -> aio.Channel:
         This property caches on the instance; repeated calls return
         the same channel.
         """
-        # Sanity check: Only create a new channel if we do not already
-        # have one.
-        if not hasattr(self, "_grpc_channel"):
-            self._grpc_channel = self.create_channel(
-                self._host, credentials=self._credentials,
-            )
-
         # Return the channel from cache.
         return self._grpc_channel
 
diff --git a/google/cloud/texttospeech_v1beta1/types/__init__.py b/google/cloud/texttospeech_v1beta1/types/__init__.py
index cb459aa3..bbb6eb00 100644
--- a/google/cloud/texttospeech_v1beta1/types/__init__.py
+++ b/google/cloud/texttospeech_v1beta1/types/__init__.py
@@ -16,26 +16,29 @@
 #
 
 from .cloud_tts import (
+    AudioConfig,
     ListVoicesRequest,
     ListVoicesResponse,
-    Voice,
-    SynthesizeSpeechRequest,
     SynthesisInput,
-    VoiceSelectionParams,
-    AudioConfig,
+    SynthesizeSpeechRequest,
     SynthesizeSpeechResponse,
     Timepoint,
+    Voice,
+    VoiceSelectionParams,
+    AudioEncoding,
+    SsmlVoiceGender,
 )
 
-
 __all__ = (
+    "AudioConfig",
     "ListVoicesRequest",
     "ListVoicesResponse",
-    "Voice",
-    "SynthesizeSpeechRequest",
     "SynthesisInput",
-    "VoiceSelectionParams",
-    "AudioConfig",
+    "SynthesizeSpeechRequest",
     "SynthesizeSpeechResponse",
     "Timepoint",
+    "Voice",
+    "VoiceSelectionParams",
+    "AudioEncoding",
+    "SsmlVoiceGender",
 )
diff --git a/google/cloud/texttospeech_v1beta1/types/cloud_tts.py b/google/cloud/texttospeech_v1beta1/types/cloud_tts.py
index 90855911..b4a46327 100644
--- a/google/cloud/texttospeech_v1beta1/types/cloud_tts.py
+++ b/google/cloud/texttospeech_v1beta1/types/cloud_tts.py
@@ -83,7 +83,7 @@ class ListVoicesResponse(proto.Message):
     r"""The message returned to the client by the ``ListVoices`` method.
 
     Attributes:
-        voices (Sequence[~.cloud_tts.Voice]):
+        voices (Sequence[google.cloud.texttospeech_v1beta1.types.Voice]):
             The list of voices.
     """
 
@@ -101,7 +101,7 @@ class Voice(proto.Message):
         name (str):
             The name of this voice.  Each distinct voice
             has a unique name.
-        ssml_gender (~.cloud_tts.SsmlVoiceGender):
+        ssml_gender (google.cloud.texttospeech_v1beta1.types.SsmlVoiceGender):
             The gender of this voice.
         natural_sample_rate_hertz (int):
             The natural sample rate (in hertz) for this
@@ -122,16 +122,16 @@ class SynthesizeSpeechRequest(proto.Message):
     ``SynthesizeSpeech`` method.
 
     Attributes:
-        input (~.cloud_tts.SynthesisInput):
+        input (google.cloud.texttospeech_v1beta1.types.SynthesisInput):
             Required. The Synthesizer requires either
             plain text or SSML as input.
-        voice (~.cloud_tts.VoiceSelectionParams):
+        voice (google.cloud.texttospeech_v1beta1.types.VoiceSelectionParams):
             Required. The desired voice of the
             synthesized audio.
-        audio_config (~.cloud_tts.AudioConfig):
+        audio_config (google.cloud.texttospeech_v1beta1.types.AudioConfig):
             Required. The configuration of the
             synthesized audio.
-        enable_time_pointing (Sequence[~.cloud_tts.SynthesizeSpeechRequest.TimepointType]):
+        enable_time_pointing (Sequence[google.cloud.texttospeech_v1beta1.types.SynthesizeSpeechRequest.TimepointType]):
             Whether and what timepoints should be
             returned in the response.
     """
@@ -199,7 +199,7 @@ class VoiceSelectionParams(proto.Message):
             The name of the voice. If not set, the service will choose a
             voice based on the other parameters such as language_code
             and gender.
-        ssml_gender (~.cloud_tts.SsmlVoiceGender):
+        ssml_gender (google.cloud.texttospeech_v1beta1.types.SsmlVoiceGender):
             The preferred gender of the voice. If not set, the service
             will choose a voice based on the other parameters such as
             language_code and name. Note that this is only a preference,
@@ -219,7 +219,7 @@ class AudioConfig(proto.Message):
     r"""Description of audio data to be synthesized.
 
     Attributes:
-        audio_encoding (~.cloud_tts.AudioEncoding):
+        audio_encoding (google.cloud.texttospeech_v1beta1.types.AudioEncoding):
             Required. The format of the audio byte
             stream.
         speaking_rate (float):
@@ -287,11 +287,11 @@ class SynthesizeSpeechResponse(proto.Message):
             include the WAV header. Note: as with all bytes fields,
             protobuffers use a pure binary representation, whereas JSON
             representations use base64.
-        timepoints (Sequence[~.cloud_tts.Timepoint]):
+        timepoints (Sequence[google.cloud.texttospeech_v1beta1.types.Timepoint]):
             A link between a position in the original request input and
             a corresponding time in the output audio. It's only
             supported via ``<mark>`` of SSML input.
-        audio_config (~.cloud_tts.AudioConfig):
+        audio_config (google.cloud.texttospeech_v1beta1.types.AudioConfig):
             The audio metadata of ``audio_content``.
     """
 
@@ -299,7 +299,7 @@ class SynthesizeSpeechResponse(proto.Message):
 
     timepoints = proto.RepeatedField(proto.MESSAGE, number=2, message="Timepoint",)
 
-    audio_config = proto.Field(proto.MESSAGE, number=4, message=AudioConfig,)
+    audio_config = proto.Field(proto.MESSAGE, number=4, message="AudioConfig",)
 
 
 class Timepoint(proto.Message):
diff --git a/noxfile.py b/noxfile.py
index 6ae48790..9249c5b9 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -27,8 +27,22 @@
 BLACK_PATHS = ["docs", "google", "tests", "noxfile.py", "setup.py"]
 
 DEFAULT_PYTHON_VERSION = "3.8"
-SYSTEM_TEST_PYTHON_VERSIONS = ["3.7"]
-UNIT_TEST_PYTHON_VERSIONS = ["3.6", "3.7", "3.8"]
+SYSTEM_TEST_PYTHON_VERSIONS = ["3.8"]
+UNIT_TEST_PYTHON_VERSIONS = ["3.6", "3.7", "3.8", "3.9"]
+
+# 'docfx' is excluded since it only needs to run in 'docs-presubmit'
+nox.options.sessions = [
+    "unit",
+    "system",
+    "cover",
+    "lint",
+    "lint_setup_py",
+    "blacken",
+    "docs",
+]
+
+# Error if a python version is missing
+nox.options.error_on_missing_interpreters = True
 
 
 @nox.session(python=DEFAULT_PYTHON_VERSION)
@@ -72,16 +86,19 @@ def default(session):
     # Install all test dependencies, then install this package in-place.
     session.install("asyncmock", "pytest-asyncio")
 
-    session.install("mock", "pytest", "pytest-cov")
+    session.install(
+        "mock", "pytest", "pytest-cov",
+    )
+
     session.install("-e", ".")
 
     # Run py.test against the unit tests.
     session.run(
         "py.test",
         "--quiet",
-        "--cov=google.cloud.texttospeech",
-        "--cov=google.cloud",
-        "--cov=tests.unit",
+        f"--junitxml=unit_{session.python}_sponge_log.xml",
+        "--cov=google/cloud",
+        "--cov=tests/unit",
         "--cov-append",
         "--cov-config=.coveragerc",
         "--cov-report=",
@@ -109,6 +126,9 @@ def system(session):
     # Sanity check: Only run tests if the environment variable is set.
     if not os.environ.get("GOOGLE_APPLICATION_CREDENTIALS", ""):
         session.skip("Credentials must be set via environment variable")
+    # Install pyopenssl for mTLS testing.
+    if os.environ.get("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true":
+        session.install("pyopenssl")
 
     system_test_exists = os.path.exists(system_test_path)
     system_test_folder_exists = os.path.exists(system_test_folder_path)
@@ -128,9 +148,21 @@ def system(session):
 
     # Run py.test against the system tests.
     if system_test_exists:
-        session.run("py.test", "--quiet", system_test_path, *session.posargs)
+        session.run(
+            "py.test",
+            "--quiet",
+            f"--junitxml=system_{session.python}_sponge_log.xml",
+            system_test_path,
+            *session.posargs,
+        )
     if system_test_folder_exists:
-        session.run("py.test", "--quiet", system_test_folder_path, *session.posargs)
+        session.run(
+            "py.test",
+            "--quiet",
+            f"--junitxml=system_{session.python}_sponge_log.xml",
+            system_test_folder_path,
+            *session.posargs,
+        )
 
 
 @nox.session(python=DEFAULT_PYTHON_VERSION)
diff --git a/renovate.json b/renovate.json
index 4fa94931..f08bc22c 100644
--- a/renovate.json
+++ b/renovate.json
@@ -1,5 +1,6 @@
 {
   "extends": [
     "config:base",  ":preserveSemverRanges"
-  ]
+  ],
+  "ignorePaths": [".pre-commit-config.yaml"]
 }
diff --git a/samples/snippets/noxfile.py b/samples/snippets/noxfile.py
index ba55d7ce..97bf7da8 100644
--- a/samples/snippets/noxfile.py
+++ b/samples/snippets/noxfile.py
@@ -17,6 +17,7 @@
 import os
 from pathlib import Path
 import sys
+from typing import Callable, Dict, List, Optional
 
 import nox
 
@@ -39,6 +40,10 @@
     # You can opt out from the test for specific Python versions.
     'ignored_versions': ["2.7"],
 
+    # Old samples are opted out of enforcing Python type hints
+    # All new samples should feature them
+    'enforce_type_hints': False,
+
     # An envvar key for determining the project id to use. Change it
     # to 'BUILD_SPECIFIC_GCLOUD_PROJECT' if you want to opt in using a
     # build specific Cloud project. You can also use your own string
@@ -64,7 +69,7 @@
 TEST_CONFIG.update(TEST_CONFIG_OVERRIDE)
 
 
-def get_pytest_env_vars():
+def get_pytest_env_vars() -> Dict[str, str]:
     """Returns a dict for pytest invocation."""
     ret = {}
 
@@ -80,7 +85,7 @@ def get_pytest_env_vars():
 
 # DO NOT EDIT - automatically generated.
 # All versions used to tested samples.
-ALL_VERSIONS = ["2.7", "3.6", "3.7", "3.8"]
+ALL_VERSIONS = ["2.7", "3.6", "3.7", "3.8", "3.9"]
 
 # Any default versions that should be ignored.
 IGNORED_VERSIONS = TEST_CONFIG['ignored_versions']
@@ -93,7 +98,7 @@ def get_pytest_env_vars():
 #
 
 
-def _determine_local_import_names(start_dir):
+def _determine_local_import_names(start_dir: str) -> List[str]:
     """Determines all import names that should be considered "local".
 
     This is used when running the linter to insure that import order is
@@ -131,8 +136,11 @@ def _determine_local_import_names(start_dir):
 
 
 @nox.session
-def lint(session):
-    session.install("flake8", "flake8-import-order")
+def lint(session: nox.sessions.Session) -> None:
+    if not TEST_CONFIG['enforce_type_hints']:
+        session.install("flake8", "flake8-import-order")
+    else:
+        session.install("flake8", "flake8-import-order", "flake8-annotations")
 
     local_names = _determine_local_import_names(".")
     args = FLAKE8_COMMON_ARGS + [
@@ -141,8 +149,18 @@ def lint(session):
         "."
     ]
     session.run("flake8", *args)
+#
+# Black
+#
 
 
+@nox.session
+def blacken(session: nox.sessions.Session) -> None:
+    session.install("black")
+    python_files = [path for path in os.listdir(".") if path.endswith(".py")]
+
+    session.run("black", *python_files)
+
 #
 # Sample Tests
 #
@@ -151,7 +169,7 @@ def lint(session):
 PYTEST_COMMON_ARGS = ["--junitxml=sponge_log.xml"]
 
 
-def _session_tests(session, post_install=None):
+def _session_tests(session: nox.sessions.Session, post_install: Callable = None) -> None:
     """Runs py.test for a particular project."""
     if os.path.exists("requirements.txt"):
         session.install("-r", "requirements.txt")
@@ -177,7 +195,7 @@ def _session_tests(session, post_install=None):
 
 
 @nox.session(python=ALL_VERSIONS)
-def py(session):
+def py(session: nox.sessions.Session) -> None:
     """Runs py.test for a sample using the specified version of Python."""
     if session.python in TESTED_VERSIONS:
         _session_tests(session)
@@ -192,7 +210,7 @@ def py(session):
 #
 
 
-def _get_repo_root():
+def _get_repo_root() -> Optional[str]:
     """ Returns the root folder of the project. """
     # Get root of this repository. Assume we don't have directories nested deeper than 10 items.
     p = Path(os.getcwd())
@@ -201,6 +219,11 @@ def _get_repo_root():
             break
         if Path(p / ".git").exists():
             return str(p)
+        # .git is not available in repos cloned via Cloud Build
+        # setup.py is always in the library's root, so use that instead
+        # https://github.com/googleapis/synthtool/issues/792
+        if Path(p / "setup.py").exists():
+            return str(p)
         p = p.parent
     raise Exception("Unable to detect repository root.")
 
@@ -210,7 +233,7 @@ def _get_repo_root():
 
 @nox.session
 @nox.parametrize("path", GENERATED_READMES)
-def readmegen(session, path):
+def readmegen(session: nox.sessions.Session, path: str) -> None:
     """(Re-)generates the readme for a sample."""
     session.install("jinja2", "pyyaml")
     dir_ = os.path.dirname(path)
diff --git a/scripts/decrypt-secrets.sh b/scripts/decrypt-secrets.sh
index ff599eb2..21f6d2a2 100755
--- a/scripts/decrypt-secrets.sh
+++ b/scripts/decrypt-secrets.sh
@@ -20,14 +20,27 @@ ROOT=$( dirname "$DIR" )
 # Work from the project root.
 cd $ROOT
 
+# Prevent it from overriding files.
+# We recommend that sample authors use their own service account files and cloud project.
+# In that case, they are supposed to prepare these files by themselves.
+if [[ -f "testing/test-env.sh" ]] || \
+       [[ -f "testing/service-account.json" ]] || \
+       [[ -f "testing/client-secrets.json" ]]; then
+    echo "One or more target files exist, aborting."
+    exit 1
+fi
+
 # Use SECRET_MANAGER_PROJECT if set, fallback to cloud-devrel-kokoro-resources.
 PROJECT_ID="${SECRET_MANAGER_PROJECT:-cloud-devrel-kokoro-resources}"
 
 gcloud secrets versions access latest --secret="python-docs-samples-test-env" \
+       --project="${PROJECT_ID}" \
        > testing/test-env.sh
 gcloud secrets versions access latest \
        --secret="python-docs-samples-service-account" \
+       --project="${PROJECT_ID}" \
        > testing/service-account.json
 gcloud secrets versions access latest \
        --secret="python-docs-samples-client-secrets" \
-       > testing/client-secrets.json
\ No newline at end of file
+       --project="${PROJECT_ID}" \
+       > testing/client-secrets.json
diff --git a/scripts/fixup_texttospeech_v1_keywords.py b/scripts/fixup_texttospeech_v1_keywords.py
index 7c548aef..09616e09 100644
--- a/scripts/fixup_texttospeech_v1_keywords.py
+++ b/scripts/fixup_texttospeech_v1_keywords.py
@@ -1,3 +1,4 @@
+#! /usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # Copyright 2020 Google LLC
diff --git a/scripts/fixup_texttospeech_v1beta1_keywords.py b/scripts/fixup_texttospeech_v1beta1_keywords.py
index b11f7d87..a69becfd 100644
--- a/scripts/fixup_texttospeech_v1beta1_keywords.py
+++ b/scripts/fixup_texttospeech_v1beta1_keywords.py
@@ -1,3 +1,4 @@
+#! /usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 # Copyright 2020 Google LLC
diff --git a/synth.metadata b/synth.metadata
index 3af3ad5e..7ce57c97 100644
--- a/synth.metadata
+++ b/synth.metadata
@@ -3,30 +3,30 @@
     {
       "git": {
         "name": ".",
-        "remote": "https://github.com/googleapis/python-texttospeech.git",
-        "sha": "97b044d0ed59483d34a86fbd99faf85a32507c4c"
+        "remote": "git@github.com:googleapis/python-texttospeech",
+        "sha": "5f6f26172a520d4791927650a624c3de6af1e7d0"
       }
     },
     {
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "4d52dfb72078000b13de923c1dadec19f3a64ad1",
-        "internalRef": "324098852"
+        "sha": "8d17d8fafbb87ac64bb3179b99ac34ed41375a51",
+        "internalRef": "363762006"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4f8f5dc24af79694887385015294e4dbb214c352"
+        "sha": "8b13da943497f75c5303700bff5aabdd85d939e0"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "4f8f5dc24af79694887385015294e4dbb214c352"
+        "sha": "8b13da943497f75c5303700bff5aabdd85d939e0"
       }
     }
   ],
@@ -37,7 +37,7 @@
         "apiName": "texttospeech",
         "apiVersion": "v1beta1",
         "language": "python",
-        "generator": "gapic-generator-python"
+        "generator": "bazel"
       }
     },
     {
@@ -46,7 +46,7 @@
         "apiName": "texttospeech",
         "apiVersion": "v1",
         "language": "python",
-        "generator": "gapic-generator-python"
+        "generator": "bazel"
       }
     }
   ]
diff --git a/synth.py b/synth.py
index d75fe43c..0e6019e2 100644
--- a/synth.py
+++ b/synth.py
@@ -19,7 +19,7 @@
 from synthtool import gcp
 from synthtool.languages import python
 
-gapic = gcp.GAPICMicrogenerator()
+gapic = gcp.GAPICBazel()
 common = gcp.CommonTemplates()
 versions = ["v1beta1", "v1"]
 
@@ -27,8 +27,13 @@
 # Generate texttospeech GAPIC layer
 # ----------------------------------------------------------------------------
 for version in versions:
-    library = gapic.py_library(service="texttospeech", version=version,)
-    s.move(library, excludes=["setup.py", "docs/index.rst"])
+    library = gapic.py_library(
+        service="texttospeech",
+        version=version,
+        bazel_target=f"//google/cloud/texttospeech/{version}:texttospeech-{version}-py",
+
+    )
+    s.move(library, excludes=["setup.py", "docs/index.rst", "README.rst"])
 
 # Sphinx interprets `*` as emphasis
 s.replace(
@@ -43,8 +48,6 @@
 templated_files = common.py_library(
     samples=True,
     microgenerator=True,
-    unit_test_python_versions=["3.6", "3.7", "3.8"],
-    system_test_python_versions=["3.7"],
 )
 s.move(templated_files, excludes=[".coveragerc"])  # microgenerator has a good .coveragerc file
 
diff --git a/tests/unit/gapic/texttospeech_v1/__init__.py b/tests/unit/gapic/texttospeech_v1/__init__.py
index 8b137891..42ffdf2b 100644
--- a/tests/unit/gapic/texttospeech_v1/__init__.py
+++ b/tests/unit/gapic/texttospeech_v1/__init__.py
@@ -1 +1,16 @@
+# -*- coding: utf-8 -*-
 
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
diff --git a/tests/unit/gapic/texttospeech_v1/test_text_to_speech.py b/tests/unit/gapic/texttospeech_v1/test_text_to_speech.py
index 5cfd08e9..9c6c48ba 100644
--- a/tests/unit/gapic/texttospeech_v1/test_text_to_speech.py
+++ b/tests/unit/gapic/texttospeech_v1/test_text_to_speech.py
@@ -80,7 +80,22 @@ def test__get_default_mtls_endpoint():
     assert TextToSpeechClient._get_default_mtls_endpoint(non_googleapi) == non_googleapi
 
 
-@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient])
+@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient,])
+def test_text_to_speech_client_from_service_account_info(client_class):
+    creds = credentials.AnonymousCredentials()
+    with mock.patch.object(
+        service_account.Credentials, "from_service_account_info"
+    ) as factory:
+        factory.return_value = creds
+        info = {"valid": True}
+        client = client_class.from_service_account_info(info)
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
+
+        assert client.transport._host == "texttospeech.googleapis.com:443"
+
+
+@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient,])
 def test_text_to_speech_client_from_service_account_file(client_class):
     creds = credentials.AnonymousCredentials()
     with mock.patch.object(
@@ -88,17 +103,22 @@ def test_text_to_speech_client_from_service_account_file(client_class):
     ) as factory:
         factory.return_value = creds
         client = client_class.from_service_account_file("dummy/file/path.json")
-        assert client._transport._credentials == creds
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
 
         client = client_class.from_service_account_json("dummy/file/path.json")
-        assert client._transport._credentials == creds
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
 
-        assert client._transport._host == "texttospeech.googleapis.com:443"
+        assert client.transport._host == "texttospeech.googleapis.com:443"
 
 
 def test_text_to_speech_client_get_transport_class():
     transport = TextToSpeechClient.get_transport_class()
-    assert transport == transports.TextToSpeechGrpcTransport
+    available_transports = [
+        transports.TextToSpeechGrpcTransport,
+    ]
+    assert transport in available_transports
 
     transport = TextToSpeechClient.get_transport_class("grpc")
     assert transport == transports.TextToSpeechGrpcTransport
@@ -147,15 +167,14 @@ def test_text_to_speech_client_client_options(
             credentials_file=None,
             host="squid.clam.whelk",
             scopes=None,
-            api_mtls_endpoint="squid.clam.whelk",
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS is
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
     # "never".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "never"}):
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never"}):
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class()
@@ -164,15 +183,14 @@ def test_text_to_speech_client_client_options(
                 credentials_file=None,
                 host=client.DEFAULT_ENDPOINT,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-                client_cert_source=None,
+                client_cert_source_for_mtls=None,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS is
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
     # "always".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "always"}):
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always"}):
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class()
@@ -181,56 +199,140 @@ def test_text_to_speech_client_client_options(
                 credentials_file=None,
                 host=client.DEFAULT_MTLS_ENDPOINT,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                client_cert_source=None,
+                client_cert_source_for_mtls=None,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", and client_cert_source is provided.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT has
+    # unsupported value.
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "Unsupported"}):
+        with pytest.raises(MutualTLSChannelError):
+            client = client_class()
+
+    # Check the case GOOGLE_API_USE_CLIENT_CERTIFICATE has unsupported value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "Unsupported"}
+    ):
+        with pytest.raises(ValueError):
+            client = client_class()
+
+    # Check the case quota_project_id is provided
+    options = client_options.ClientOptions(quota_project_id="octopus")
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file=None,
+            host=client.DEFAULT_ENDPOINT,
+            scopes=None,
+            client_cert_source_for_mtls=None,
+            quota_project_id="octopus",
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+        )
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name,use_client_cert_env",
+    [
+        (TextToSpeechClient, transports.TextToSpeechGrpcTransport, "grpc", "true"),
+        (
+            TextToSpeechAsyncClient,
+            transports.TextToSpeechGrpcAsyncIOTransport,
+            "grpc_asyncio",
+            "true",
+        ),
+        (TextToSpeechClient, transports.TextToSpeechGrpcTransport, "grpc", "false"),
+        (
+            TextToSpeechAsyncClient,
+            transports.TextToSpeechGrpcAsyncIOTransport,
+            "grpc_asyncio",
+            "false",
+        ),
+    ],
+)
+@mock.patch.object(
+    TextToSpeechClient, "DEFAULT_ENDPOINT", modify_default_endpoint(TextToSpeechClient)
+)
+@mock.patch.object(
+    TextToSpeechAsyncClient,
+    "DEFAULT_ENDPOINT",
+    modify_default_endpoint(TextToSpeechAsyncClient),
+)
+@mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "auto"})
+def test_text_to_speech_client_mtls_env_auto(
+    client_class, transport_class, transport_name, use_client_cert_env
+):
+    # This tests the endpoint autoswitch behavior. Endpoint is autoswitched to the default
+    # mtls endpoint, if GOOGLE_API_USE_CLIENT_CERTIFICATE is "true" and client cert exists.
+
+    # Check the case client_cert_source is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         options = client_options.ClientOptions(
             client_cert_source=client_cert_source_callback
         )
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class(client_options=options)
+
+            if use_client_cert_env == "false":
+                expected_client_cert_source = None
+                expected_host = client.DEFAULT_ENDPOINT
+            else:
+                expected_client_cert_source = client_cert_source_callback
+                expected_host = client.DEFAULT_MTLS_ENDPOINT
+
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
-                host=client.DEFAULT_MTLS_ENDPOINT,
+                host=expected_host,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                client_cert_source=client_cert_source_callback,
+                client_cert_source_for_mtls=expected_client_cert_source,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", and default_client_cert_source is provided.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+    # Check the case ADC client cert is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         with mock.patch.object(transport_class, "__init__") as patched:
             with mock.patch(
                 "google.auth.transport.mtls.has_default_client_cert_source",
                 return_value=True,
             ):
-                patched.return_value = None
-                client = client_class()
-                patched.assert_called_once_with(
-                    credentials=None,
-                    credentials_file=None,
-                    host=client.DEFAULT_MTLS_ENDPOINT,
-                    scopes=None,
-                    api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                    client_cert_source=None,
-                    quota_project_id=None,
-                    client_info=transports.base.DEFAULT_CLIENT_INFO,
-                )
-
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", but client_cert_source and default_client_cert_source are None.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+                with mock.patch(
+                    "google.auth.transport.mtls.default_client_cert_source",
+                    return_value=client_cert_source_callback,
+                ):
+                    if use_client_cert_env == "false":
+                        expected_host = client.DEFAULT_ENDPOINT
+                        expected_client_cert_source = None
+                    else:
+                        expected_host = client.DEFAULT_MTLS_ENDPOINT
+                        expected_client_cert_source = client_cert_source_callback
+
+                    patched.return_value = None
+                    client = client_class()
+                    patched.assert_called_once_with(
+                        credentials=None,
+                        credentials_file=None,
+                        host=expected_host,
+                        scopes=None,
+                        client_cert_source_for_mtls=expected_client_cert_source,
+                        quota_project_id=None,
+                        client_info=transports.base.DEFAULT_CLIENT_INFO,
+                    )
+
+    # Check the case client_cert_source and ADC client cert are not provided.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         with mock.patch.object(transport_class, "__init__") as patched:
             with mock.patch(
                 "google.auth.transport.mtls.has_default_client_cert_source",
@@ -243,34 +345,11 @@ def test_text_to_speech_client_client_options(
                     credentials_file=None,
                     host=client.DEFAULT_ENDPOINT,
                     scopes=None,
-                    api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-                    client_cert_source=None,
+                    client_cert_source_for_mtls=None,
                     quota_project_id=None,
                     client_info=transports.base.DEFAULT_CLIENT_INFO,
                 )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS has
-    # unsupported value.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "Unsupported"}):
-        with pytest.raises(MutualTLSChannelError):
-            client = client_class()
-
-    # Check the case quota_project_id is provided
-    options = client_options.ClientOptions(quota_project_id="octopus")
-    with mock.patch.object(transport_class, "__init__") as patched:
-        patched.return_value = None
-        client = client_class(client_options=options)
-        patched.assert_called_once_with(
-            credentials=None,
-            credentials_file=None,
-            host=client.DEFAULT_ENDPOINT,
-            scopes=None,
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
-            quota_project_id="octopus",
-            client_info=transports.base.DEFAULT_CLIENT_INFO,
-        )
-
 
 @pytest.mark.parametrize(
     "client_class,transport_class,transport_name",
@@ -296,8 +375,7 @@ def test_text_to_speech_client_client_options_scopes(
             credentials_file=None,
             host=client.DEFAULT_ENDPOINT,
             scopes=["1", "2"],
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -327,8 +405,7 @@ def test_text_to_speech_client_client_options_credentials_file(
             credentials_file="credentials.json",
             host=client.DEFAULT_ENDPOINT,
             scopes=None,
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -345,8 +422,7 @@ def test_text_to_speech_client_client_options_from_dict():
             credentials_file=None,
             host="squid.clam.whelk",
             scopes=None,
-            api_mtls_endpoint="squid.clam.whelk",
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -362,7 +438,7 @@ def test_list_voices(transport: str = "grpc", request_type=cloud_tts.ListVoicesR
     request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(type(client._transport.list_voices), "__call__") as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -375,6 +451,7 @@ def test_list_voices(transport: str = "grpc", request_type=cloud_tts.ListVoicesR
         assert args[0] == cloud_tts.ListVoicesRequest()
 
     # Establish that the response is the type that we expect.
+
     assert isinstance(response, cloud_tts.ListVoicesResponse)
 
 
@@ -382,20 +459,36 @@ def test_list_voices_from_dict():
     test_list_voices(request_type=dict)
 
 
+def test_list_voices_empty_call():
+    # This test is a coverage failsafe to make sure that totally empty calls,
+    # i.e. request == None and no flattened fields passed, work.
+    client = TextToSpeechClient(
+        credentials=credentials.AnonymousCredentials(), transport="grpc",
+    )
+
+    # Mock the actual call within the gRPC stub, and fake the request.
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
+        client.list_voices()
+        call.assert_called()
+        _, args, _ = call.mock_calls[0]
+
+        assert args[0] == cloud_tts.ListVoicesRequest()
+
+
 @pytest.mark.asyncio
-async def test_list_voices_async(transport: str = "grpc_asyncio"):
+async def test_list_voices_async(
+    transport: str = "grpc_asyncio", request_type=cloud_tts.ListVoicesRequest
+):
     client = TextToSpeechAsyncClient(
         credentials=credentials.AnonymousCredentials(), transport=transport,
     )
 
     # Everything is optional in proto3 as far as the runtime is concerned,
     # and we are mocking out the actual API, so just send an empty request.
-    request = cloud_tts.ListVoicesRequest()
+    request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(
-        type(client._client._transport.list_voices), "__call__"
-    ) as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(
             cloud_tts.ListVoicesResponse()
@@ -407,17 +500,22 @@ async def test_list_voices_async(transport: str = "grpc_asyncio"):
         assert len(call.mock_calls)
         _, args, _ = call.mock_calls[0]
 
-        assert args[0] == request
+        assert args[0] == cloud_tts.ListVoicesRequest()
 
     # Establish that the response is the type that we expect.
     assert isinstance(response, cloud_tts.ListVoicesResponse)
 
 
+@pytest.mark.asyncio
+async def test_list_voices_async_from_dict():
+    await test_list_voices_async(request_type=dict)
+
+
 def test_list_voices_flattened():
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(type(client._transport.list_voices), "__call__") as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -449,9 +547,7 @@ async def test_list_voices_flattened_async():
     client = TextToSpeechAsyncClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(
-        type(client._client._transport.list_voices), "__call__"
-    ) as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -495,7 +591,7 @@ def test_synthesize_speech(
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse(
@@ -511,6 +607,7 @@ def test_synthesize_speech(
         assert args[0] == cloud_tts.SynthesizeSpeechRequest()
 
     # Establish that the response is the type that we expect.
+
     assert isinstance(response, cloud_tts.SynthesizeSpeechResponse)
 
     assert response.audio_content == b"audio_content_blob"
@@ -520,19 +617,39 @@ def test_synthesize_speech_from_dict():
     test_synthesize_speech(request_type=dict)
 
 
+def test_synthesize_speech_empty_call():
+    # This test is a coverage failsafe to make sure that totally empty calls,
+    # i.e. request == None and no flattened fields passed, work.
+    client = TextToSpeechClient(
+        credentials=credentials.AnonymousCredentials(), transport="grpc",
+    )
+
+    # Mock the actual call within the gRPC stub, and fake the request.
+    with mock.patch.object(
+        type(client.transport.synthesize_speech), "__call__"
+    ) as call:
+        client.synthesize_speech()
+        call.assert_called()
+        _, args, _ = call.mock_calls[0]
+
+        assert args[0] == cloud_tts.SynthesizeSpeechRequest()
+
+
 @pytest.mark.asyncio
-async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
+async def test_synthesize_speech_async(
+    transport: str = "grpc_asyncio", request_type=cloud_tts.SynthesizeSpeechRequest
+):
     client = TextToSpeechAsyncClient(
         credentials=credentials.AnonymousCredentials(), transport=transport,
     )
 
     # Everything is optional in proto3 as far as the runtime is concerned,
     # and we are mocking out the actual API, so just send an empty request.
-    request = cloud_tts.SynthesizeSpeechRequest()
+    request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(
@@ -545,7 +662,7 @@ async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
         assert len(call.mock_calls)
         _, args, _ = call.mock_calls[0]
 
-        assert args[0] == request
+        assert args[0] == cloud_tts.SynthesizeSpeechRequest()
 
     # Establish that the response is the type that we expect.
     assert isinstance(response, cloud_tts.SynthesizeSpeechResponse)
@@ -553,12 +670,17 @@ async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
     assert response.audio_content == b"audio_content_blob"
 
 
+@pytest.mark.asyncio
+async def test_synthesize_speech_async_from_dict():
+    await test_synthesize_speech_async(request_type=dict)
+
+
 def test_synthesize_speech_flattened():
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse()
@@ -611,7 +733,7 @@ async def test_synthesize_speech_flattened_async():
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse()
@@ -698,7 +820,7 @@ def test_transport_instance():
         credentials=credentials.AnonymousCredentials(),
     )
     client = TextToSpeechClient(transport=transport)
-    assert client._transport is transport
+    assert client.transport is transport
 
 
 def test_transport_get_channel():
@@ -716,10 +838,25 @@ def test_transport_get_channel():
     assert channel
 
 
+@pytest.mark.parametrize(
+    "transport_class",
+    [
+        transports.TextToSpeechGrpcTransport,
+        transports.TextToSpeechGrpcAsyncIOTransport,
+    ],
+)
+def test_transport_adc(transport_class):
+    # Test default credentials are used if not provided.
+    with mock.patch.object(auth, "default") as adc:
+        adc.return_value = (credentials.AnonymousCredentials(), None)
+        transport_class()
+        adc.assert_called_once()
+
+
 def test_transport_grpc_default():
     # A client should use the gRPC transport by default.
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
-    assert isinstance(client._transport, transports.TextToSpeechGrpcTransport,)
+    assert isinstance(client.transport, transports.TextToSpeechGrpcTransport,)
 
 
 def test_text_to_speech_base_transport_error():
@@ -771,6 +908,17 @@ def test_text_to_speech_base_transport_with_credentials_file():
         )
 
 
+def test_text_to_speech_base_transport_with_adc():
+    # Test the default credentials are used if credentials and credentials_file are None.
+    with mock.patch.object(auth, "default") as adc, mock.patch(
+        "google.cloud.texttospeech_v1.services.text_to_speech.transports.TextToSpeechTransport._prep_wrapped_messages"
+    ) as Transport:
+        Transport.return_value = None
+        adc.return_value = (credentials.AnonymousCredentials(), None)
+        transport = transports.TextToSpeechTransport()
+        adc.assert_called_once()
+
+
 def test_text_to_speech_auth_adc():
     # If no credentials are provided, we should use ADC credentials.
     with mock.patch.object(auth, "default") as adc:
@@ -796,6 +944,48 @@ def test_text_to_speech_transport_auth_adc():
         )
 
 
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_grpc_transport_client_cert_source_for_mtls(transport_class):
+    cred = credentials.AnonymousCredentials()
+
+    # Check ssl_channel_credentials is used if provided.
+    with mock.patch.object(transport_class, "create_channel") as mock_create_channel:
+        mock_ssl_channel_creds = mock.Mock()
+        transport_class(
+            host="squid.clam.whelk",
+            credentials=cred,
+            ssl_channel_credentials=mock_ssl_channel_creds,
+        )
+        mock_create_channel.assert_called_once_with(
+            "squid.clam.whelk:443",
+            credentials=cred,
+            credentials_file=None,
+            scopes=("https://www.googleapis.com/auth/cloud-platform",),
+            ssl_credentials=mock_ssl_channel_creds,
+            quota_project_id=None,
+            options=[
+                ("grpc.max_send_message_length", -1),
+                ("grpc.max_receive_message_length", -1),
+            ],
+        )
+
+    # Check if ssl_channel_credentials is not provided, then client_cert_source_for_mtls
+    # is used.
+    with mock.patch.object(transport_class, "create_channel", return_value=mock.Mock()):
+        with mock.patch("grpc.ssl_channel_credentials") as mock_ssl_cred:
+            transport_class(
+                credentials=cred,
+                client_cert_source_for_mtls=client_cert_source_callback,
+            )
+            expected_cert, expected_key = client_cert_source_callback()
+            mock_ssl_cred.assert_called_once_with(
+                certificate_chain=expected_cert, private_key=expected_key
+            )
+
+
 def test_text_to_speech_host_no_port():
     client = TextToSpeechClient(
         credentials=credentials.AnonymousCredentials(),
@@ -803,7 +993,7 @@ def test_text_to_speech_host_no_port():
             api_endpoint="texttospeech.googleapis.com"
         ),
     )
-    assert client._transport._host == "texttospeech.googleapis.com:443"
+    assert client.transport._host == "texttospeech.googleapis.com:443"
 
 
 def test_text_to_speech_host_with_port():
@@ -813,185 +1003,224 @@ def test_text_to_speech_host_with_port():
             api_endpoint="texttospeech.googleapis.com:8000"
         ),
     )
-    assert client._transport._host == "texttospeech.googleapis.com:8000"
+    assert client.transport._host == "texttospeech.googleapis.com:8000"
 
 
 def test_text_to_speech_grpc_transport_channel():
-    channel = grpc.insecure_channel("http://localhost/")
+    channel = grpc.secure_channel("http://localhost/", grpc.local_channel_credentials())
 
-    # Check that if channel is provided, mtls endpoint and client_cert_source
-    # won't be used.
-    callback = mock.MagicMock()
+    # Check that channel is used if provided.
     transport = transports.TextToSpeechGrpcTransport(
-        host="squid.clam.whelk",
-        channel=channel,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=callback,
+        host="squid.clam.whelk", channel=channel,
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
-    assert not callback.called
+    assert transport._ssl_channel_credentials == None
 
 
 def test_text_to_speech_grpc_asyncio_transport_channel():
-    channel = aio.insecure_channel("http://localhost/")
+    channel = aio.secure_channel("http://localhost/", grpc.local_channel_credentials())
 
-    # Check that if channel is provided, mtls endpoint and client_cert_source
-    # won't be used.
-    callback = mock.MagicMock()
+    # Check that channel is used if provided.
     transport = transports.TextToSpeechGrpcAsyncIOTransport(
-        host="squid.clam.whelk",
-        channel=channel,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=callback,
+        host="squid.clam.whelk", channel=channel,
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
-    assert not callback.called
+    assert transport._ssl_channel_credentials == None
 
 
-@mock.patch("grpc.ssl_channel_credentials", autospec=True)
-@mock.patch("google.api_core.grpc_helpers.create_channel", autospec=True)
-def test_text_to_speech_grpc_transport_channel_mtls_with_client_cert_source(
-    grpc_create_channel, grpc_ssl_channel_cred
-):
-    # Check that if channel is None, but api_mtls_endpoint and client_cert_source
-    # are provided, then a mTLS channel will be created.
-    mock_cred = mock.Mock()
+# Remove this test when deprecated arguments (api_mtls_endpoint, client_cert_source) are
+# removed from grpc/grpc_asyncio transport constructor.
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_transport_channel_mtls_with_client_cert_source(transport_class):
+    with mock.patch(
+        "grpc.ssl_channel_credentials", autospec=True
+    ) as grpc_ssl_channel_cred:
+        with mock.patch.object(
+            transport_class, "create_channel"
+        ) as grpc_create_channel:
+            mock_ssl_cred = mock.Mock()
+            grpc_ssl_channel_cred.return_value = mock_ssl_cred
+
+            mock_grpc_channel = mock.Mock()
+            grpc_create_channel.return_value = mock_grpc_channel
+
+            cred = credentials.AnonymousCredentials()
+            with pytest.warns(DeprecationWarning):
+                with mock.patch.object(auth, "default") as adc:
+                    adc.return_value = (cred, None)
+                    transport = transport_class(
+                        host="squid.clam.whelk",
+                        api_mtls_endpoint="mtls.squid.clam.whelk",
+                        client_cert_source=client_cert_source_callback,
+                    )
+                    adc.assert_called_once()
+
+            grpc_ssl_channel_cred.assert_called_once_with(
+                certificate_chain=b"cert bytes", private_key=b"key bytes"
+            )
+            grpc_create_channel.assert_called_once_with(
+                "mtls.squid.clam.whelk:443",
+                credentials=cred,
+                credentials_file=None,
+                scopes=("https://www.googleapis.com/auth/cloud-platform",),
+                ssl_credentials=mock_ssl_cred,
+                quota_project_id=None,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            assert transport.grpc_channel == mock_grpc_channel
+            assert transport._ssl_channel_credentials == mock_ssl_cred
+
 
+# Remove this test when deprecated arguments (api_mtls_endpoint, client_cert_source) are
+# removed from grpc/grpc_asyncio transport constructor.
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_transport_channel_mtls_with_adc(transport_class):
     mock_ssl_cred = mock.Mock()
-    grpc_ssl_channel_cred.return_value = mock_ssl_cred
+    with mock.patch.multiple(
+        "google.auth.transport.grpc.SslCredentials",
+        __init__=mock.Mock(return_value=None),
+        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
+    ):
+        with mock.patch.object(
+            transport_class, "create_channel"
+        ) as grpc_create_channel:
+            mock_grpc_channel = mock.Mock()
+            grpc_create_channel.return_value = mock_grpc_channel
+            mock_cred = mock.Mock()
+
+            with pytest.warns(DeprecationWarning):
+                transport = transport_class(
+                    host="squid.clam.whelk",
+                    credentials=mock_cred,
+                    api_mtls_endpoint="mtls.squid.clam.whelk",
+                    client_cert_source=None,
+                )
 
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
+            grpc_create_channel.assert_called_once_with(
+                "mtls.squid.clam.whelk:443",
+                credentials=mock_cred,
+                credentials_file=None,
+                scopes=("https://www.googleapis.com/auth/cloud-platform",),
+                ssl_credentials=mock_ssl_cred,
+                quota_project_id=None,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            assert transport.grpc_channel == mock_grpc_channel
 
-    transport = transports.TextToSpeechGrpcTransport(
-        host="squid.clam.whelk",
-        credentials=mock_cred,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=client_cert_source_callback,
-    )
-    grpc_ssl_channel_cred.assert_called_once_with(
-        certificate_chain=b"cert bytes", private_key=b"key bytes"
-    )
-    grpc_create_channel.assert_called_once_with(
-        "mtls.squid.clam.whelk:443",
-        credentials=mock_cred,
-        credentials_file=None,
-        scopes=("https://www.googleapis.com/auth/cloud-platform",),
-        ssl_credentials=mock_ssl_cred,
-        quota_project_id=None,
+
+def test_common_billing_account_path():
+    billing_account = "squid"
+
+    expected = "billingAccounts/{billing_account}".format(
+        billing_account=billing_account,
     )
-    assert transport.grpc_channel == mock_grpc_channel
+    actual = TextToSpeechClient.common_billing_account_path(billing_account)
+    assert expected == actual
 
 
-@mock.patch("grpc.ssl_channel_credentials", autospec=True)
-@mock.patch("google.api_core.grpc_helpers_async.create_channel", autospec=True)
-def test_text_to_speech_grpc_asyncio_transport_channel_mtls_with_client_cert_source(
-    grpc_create_channel, grpc_ssl_channel_cred
-):
-    # Check that if channel is None, but api_mtls_endpoint and client_cert_source
-    # are provided, then a mTLS channel will be created.
-    mock_cred = mock.Mock()
+def test_parse_common_billing_account_path():
+    expected = {
+        "billing_account": "clam",
+    }
+    path = TextToSpeechClient.common_billing_account_path(**expected)
 
-    mock_ssl_cred = mock.Mock()
-    grpc_ssl_channel_cred.return_value = mock_ssl_cred
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_billing_account_path(path)
+    assert expected == actual
 
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    transport = transports.TextToSpeechGrpcAsyncIOTransport(
-        host="squid.clam.whelk",
-        credentials=mock_cred,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=client_cert_source_callback,
-    )
-    grpc_ssl_channel_cred.assert_called_once_with(
-        certificate_chain=b"cert bytes", private_key=b"key bytes"
-    )
-    grpc_create_channel.assert_called_once_with(
-        "mtls.squid.clam.whelk:443",
-        credentials=mock_cred,
-        credentials_file=None,
-        scopes=("https://www.googleapis.com/auth/cloud-platform",),
-        ssl_credentials=mock_ssl_cred,
-        quota_project_id=None,
-    )
-    assert transport.grpc_channel == mock_grpc_channel
+def test_common_folder_path():
+    folder = "whelk"
 
+    expected = "folders/{folder}".format(folder=folder,)
+    actual = TextToSpeechClient.common_folder_path(folder)
+    assert expected == actual
 
-@pytest.mark.parametrize(
-    "api_mtls_endpoint", ["mtls.squid.clam.whelk", "mtls.squid.clam.whelk:443"]
-)
-@mock.patch("google.api_core.grpc_helpers.create_channel", autospec=True)
-def test_text_to_speech_grpc_transport_channel_mtls_with_adc(
-    grpc_create_channel, api_mtls_endpoint
-):
-    # Check that if channel and client_cert_source are None, but api_mtls_endpoint
-    # is provided, then a mTLS channel will be created with SSL ADC.
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    # Mock google.auth.transport.grpc.SslCredentials class.
-    mock_ssl_cred = mock.Mock()
-    with mock.patch.multiple(
-        "google.auth.transport.grpc.SslCredentials",
-        __init__=mock.Mock(return_value=None),
-        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
-    ):
-        mock_cred = mock.Mock()
-        transport = transports.TextToSpeechGrpcTransport(
-            host="squid.clam.whelk",
-            credentials=mock_cred,
-            api_mtls_endpoint=api_mtls_endpoint,
-            client_cert_source=None,
-        )
-        grpc_create_channel.assert_called_once_with(
-            "mtls.squid.clam.whelk:443",
-            credentials=mock_cred,
-            credentials_file=None,
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            ssl_credentials=mock_ssl_cred,
-            quota_project_id=None,
-        )
-        assert transport.grpc_channel == mock_grpc_channel
+def test_parse_common_folder_path():
+    expected = {
+        "folder": "octopus",
+    }
+    path = TextToSpeechClient.common_folder_path(**expected)
 
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_folder_path(path)
+    assert expected == actual
 
-@pytest.mark.parametrize(
-    "api_mtls_endpoint", ["mtls.squid.clam.whelk", "mtls.squid.clam.whelk:443"]
-)
-@mock.patch("google.api_core.grpc_helpers_async.create_channel", autospec=True)
-def test_text_to_speech_grpc_asyncio_transport_channel_mtls_with_adc(
-    grpc_create_channel, api_mtls_endpoint
-):
-    # Check that if channel and client_cert_source are None, but api_mtls_endpoint
-    # is provided, then a mTLS channel will be created with SSL ADC.
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    # Mock google.auth.transport.grpc.SslCredentials class.
-    mock_ssl_cred = mock.Mock()
-    with mock.patch.multiple(
-        "google.auth.transport.grpc.SslCredentials",
-        __init__=mock.Mock(return_value=None),
-        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
-    ):
-        mock_cred = mock.Mock()
-        transport = transports.TextToSpeechGrpcAsyncIOTransport(
-            host="squid.clam.whelk",
-            credentials=mock_cred,
-            api_mtls_endpoint=api_mtls_endpoint,
-            client_cert_source=None,
-        )
-        grpc_create_channel.assert_called_once_with(
-            "mtls.squid.clam.whelk:443",
-            credentials=mock_cred,
-            credentials_file=None,
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            ssl_credentials=mock_ssl_cred,
-            quota_project_id=None,
-        )
-        assert transport.grpc_channel == mock_grpc_channel
+def test_common_organization_path():
+    organization = "oyster"
+
+    expected = "organizations/{organization}".format(organization=organization,)
+    actual = TextToSpeechClient.common_organization_path(organization)
+    assert expected == actual
+
+
+def test_parse_common_organization_path():
+    expected = {
+        "organization": "nudibranch",
+    }
+    path = TextToSpeechClient.common_organization_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_organization_path(path)
+    assert expected == actual
+
+
+def test_common_project_path():
+    project = "cuttlefish"
+
+    expected = "projects/{project}".format(project=project,)
+    actual = TextToSpeechClient.common_project_path(project)
+    assert expected == actual
+
+
+def test_parse_common_project_path():
+    expected = {
+        "project": "mussel",
+    }
+    path = TextToSpeechClient.common_project_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_project_path(path)
+    assert expected == actual
+
+
+def test_common_location_path():
+    project = "winkle"
+    location = "nautilus"
+
+    expected = "projects/{project}/locations/{location}".format(
+        project=project, location=location,
+    )
+    actual = TextToSpeechClient.common_location_path(project, location)
+    assert expected == actual
+
+
+def test_parse_common_location_path():
+    expected = {
+        "project": "scallop",
+        "location": "abalone",
+    }
+    path = TextToSpeechClient.common_location_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_location_path(path)
+    assert expected == actual
 
 
 def test_client_withDEFAULT_CLIENT_INFO():
diff --git a/tests/unit/gapic/texttospeech_v1beta1/__init__.py b/tests/unit/gapic/texttospeech_v1beta1/__init__.py
index 8b137891..42ffdf2b 100644
--- a/tests/unit/gapic/texttospeech_v1beta1/__init__.py
+++ b/tests/unit/gapic/texttospeech_v1beta1/__init__.py
@@ -1 +1,16 @@
+# -*- coding: utf-8 -*-
 
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
diff --git a/tests/unit/gapic/texttospeech_v1beta1/test_text_to_speech.py b/tests/unit/gapic/texttospeech_v1beta1/test_text_to_speech.py
index 73e6e676..a716482e 100644
--- a/tests/unit/gapic/texttospeech_v1beta1/test_text_to_speech.py
+++ b/tests/unit/gapic/texttospeech_v1beta1/test_text_to_speech.py
@@ -82,7 +82,22 @@ def test__get_default_mtls_endpoint():
     assert TextToSpeechClient._get_default_mtls_endpoint(non_googleapi) == non_googleapi
 
 
-@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient])
+@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient,])
+def test_text_to_speech_client_from_service_account_info(client_class):
+    creds = credentials.AnonymousCredentials()
+    with mock.patch.object(
+        service_account.Credentials, "from_service_account_info"
+    ) as factory:
+        factory.return_value = creds
+        info = {"valid": True}
+        client = client_class.from_service_account_info(info)
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
+
+        assert client.transport._host == "texttospeech.googleapis.com:443"
+
+
+@pytest.mark.parametrize("client_class", [TextToSpeechClient, TextToSpeechAsyncClient,])
 def test_text_to_speech_client_from_service_account_file(client_class):
     creds = credentials.AnonymousCredentials()
     with mock.patch.object(
@@ -90,17 +105,22 @@ def test_text_to_speech_client_from_service_account_file(client_class):
     ) as factory:
         factory.return_value = creds
         client = client_class.from_service_account_file("dummy/file/path.json")
-        assert client._transport._credentials == creds
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
 
         client = client_class.from_service_account_json("dummy/file/path.json")
-        assert client._transport._credentials == creds
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
 
-        assert client._transport._host == "texttospeech.googleapis.com:443"
+        assert client.transport._host == "texttospeech.googleapis.com:443"
 
 
 def test_text_to_speech_client_get_transport_class():
     transport = TextToSpeechClient.get_transport_class()
-    assert transport == transports.TextToSpeechGrpcTransport
+    available_transports = [
+        transports.TextToSpeechGrpcTransport,
+    ]
+    assert transport in available_transports
 
     transport = TextToSpeechClient.get_transport_class("grpc")
     assert transport == transports.TextToSpeechGrpcTransport
@@ -149,15 +169,14 @@ def test_text_to_speech_client_client_options(
             credentials_file=None,
             host="squid.clam.whelk",
             scopes=None,
-            api_mtls_endpoint="squid.clam.whelk",
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS is
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
     # "never".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "never"}):
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never"}):
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class()
@@ -166,15 +185,14 @@ def test_text_to_speech_client_client_options(
                 credentials_file=None,
                 host=client.DEFAULT_ENDPOINT,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-                client_cert_source=None,
+                client_cert_source_for_mtls=None,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS is
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
     # "always".
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "always"}):
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always"}):
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class()
@@ -183,56 +201,140 @@ def test_text_to_speech_client_client_options(
                 credentials_file=None,
                 host=client.DEFAULT_MTLS_ENDPOINT,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                client_cert_source=None,
+                client_cert_source_for_mtls=None,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", and client_cert_source is provided.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT has
+    # unsupported value.
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "Unsupported"}):
+        with pytest.raises(MutualTLSChannelError):
+            client = client_class()
+
+    # Check the case GOOGLE_API_USE_CLIENT_CERTIFICATE has unsupported value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "Unsupported"}
+    ):
+        with pytest.raises(ValueError):
+            client = client_class()
+
+    # Check the case quota_project_id is provided
+    options = client_options.ClientOptions(quota_project_id="octopus")
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file=None,
+            host=client.DEFAULT_ENDPOINT,
+            scopes=None,
+            client_cert_source_for_mtls=None,
+            quota_project_id="octopus",
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+        )
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name,use_client_cert_env",
+    [
+        (TextToSpeechClient, transports.TextToSpeechGrpcTransport, "grpc", "true"),
+        (
+            TextToSpeechAsyncClient,
+            transports.TextToSpeechGrpcAsyncIOTransport,
+            "grpc_asyncio",
+            "true",
+        ),
+        (TextToSpeechClient, transports.TextToSpeechGrpcTransport, "grpc", "false"),
+        (
+            TextToSpeechAsyncClient,
+            transports.TextToSpeechGrpcAsyncIOTransport,
+            "grpc_asyncio",
+            "false",
+        ),
+    ],
+)
+@mock.patch.object(
+    TextToSpeechClient, "DEFAULT_ENDPOINT", modify_default_endpoint(TextToSpeechClient)
+)
+@mock.patch.object(
+    TextToSpeechAsyncClient,
+    "DEFAULT_ENDPOINT",
+    modify_default_endpoint(TextToSpeechAsyncClient),
+)
+@mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "auto"})
+def test_text_to_speech_client_mtls_env_auto(
+    client_class, transport_class, transport_name, use_client_cert_env
+):
+    # This tests the endpoint autoswitch behavior. Endpoint is autoswitched to the default
+    # mtls endpoint, if GOOGLE_API_USE_CLIENT_CERTIFICATE is "true" and client cert exists.
+
+    # Check the case client_cert_source is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         options = client_options.ClientOptions(
             client_cert_source=client_cert_source_callback
         )
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
             client = client_class(client_options=options)
+
+            if use_client_cert_env == "false":
+                expected_client_cert_source = None
+                expected_host = client.DEFAULT_ENDPOINT
+            else:
+                expected_client_cert_source = client_cert_source_callback
+                expected_host = client.DEFAULT_MTLS_ENDPOINT
+
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
-                host=client.DEFAULT_MTLS_ENDPOINT,
+                host=expected_host,
                 scopes=None,
-                api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                client_cert_source=client_cert_source_callback,
+                client_cert_source_for_mtls=expected_client_cert_source,
                 quota_project_id=None,
                 client_info=transports.base.DEFAULT_CLIENT_INFO,
             )
 
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", and default_client_cert_source is provided.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+    # Check the case ADC client cert is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         with mock.patch.object(transport_class, "__init__") as patched:
             with mock.patch(
                 "google.auth.transport.mtls.has_default_client_cert_source",
                 return_value=True,
             ):
-                patched.return_value = None
-                client = client_class()
-                patched.assert_called_once_with(
-                    credentials=None,
-                    credentials_file=None,
-                    host=client.DEFAULT_MTLS_ENDPOINT,
-                    scopes=None,
-                    api_mtls_endpoint=client.DEFAULT_MTLS_ENDPOINT,
-                    client_cert_source=None,
-                    quota_project_id=None,
-                    client_info=transports.base.DEFAULT_CLIENT_INFO,
-                )
-
-    # Check the case api_endpoint is not provided, GOOGLE_API_USE_MTLS is
-    # "auto", but client_cert_source and default_client_cert_source are None.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "auto"}):
+                with mock.patch(
+                    "google.auth.transport.mtls.default_client_cert_source",
+                    return_value=client_cert_source_callback,
+                ):
+                    if use_client_cert_env == "false":
+                        expected_host = client.DEFAULT_ENDPOINT
+                        expected_client_cert_source = None
+                    else:
+                        expected_host = client.DEFAULT_MTLS_ENDPOINT
+                        expected_client_cert_source = client_cert_source_callback
+
+                    patched.return_value = None
+                    client = client_class()
+                    patched.assert_called_once_with(
+                        credentials=None,
+                        credentials_file=None,
+                        host=expected_host,
+                        scopes=None,
+                        client_cert_source_for_mtls=expected_client_cert_source,
+                        quota_project_id=None,
+                        client_info=transports.base.DEFAULT_CLIENT_INFO,
+                    )
+
+    # Check the case client_cert_source and ADC client cert are not provided.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
         with mock.patch.object(transport_class, "__init__") as patched:
             with mock.patch(
                 "google.auth.transport.mtls.has_default_client_cert_source",
@@ -245,34 +347,11 @@ def test_text_to_speech_client_client_options(
                     credentials_file=None,
                     host=client.DEFAULT_ENDPOINT,
                     scopes=None,
-                    api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-                    client_cert_source=None,
+                    client_cert_source_for_mtls=None,
                     quota_project_id=None,
                     client_info=transports.base.DEFAULT_CLIENT_INFO,
                 )
 
-    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS has
-    # unsupported value.
-    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS": "Unsupported"}):
-        with pytest.raises(MutualTLSChannelError):
-            client = client_class()
-
-    # Check the case quota_project_id is provided
-    options = client_options.ClientOptions(quota_project_id="octopus")
-    with mock.patch.object(transport_class, "__init__") as patched:
-        patched.return_value = None
-        client = client_class(client_options=options)
-        patched.assert_called_once_with(
-            credentials=None,
-            credentials_file=None,
-            host=client.DEFAULT_ENDPOINT,
-            scopes=None,
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
-            quota_project_id="octopus",
-            client_info=transports.base.DEFAULT_CLIENT_INFO,
-        )
-
 
 @pytest.mark.parametrize(
     "client_class,transport_class,transport_name",
@@ -298,8 +377,7 @@ def test_text_to_speech_client_client_options_scopes(
             credentials_file=None,
             host=client.DEFAULT_ENDPOINT,
             scopes=["1", "2"],
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -329,8 +407,7 @@ def test_text_to_speech_client_client_options_credentials_file(
             credentials_file="credentials.json",
             host=client.DEFAULT_ENDPOINT,
             scopes=None,
-            api_mtls_endpoint=client.DEFAULT_ENDPOINT,
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -347,8 +424,7 @@ def test_text_to_speech_client_client_options_from_dict():
             credentials_file=None,
             host="squid.clam.whelk",
             scopes=None,
-            api_mtls_endpoint="squid.clam.whelk",
-            client_cert_source=None,
+            client_cert_source_for_mtls=None,
             quota_project_id=None,
             client_info=transports.base.DEFAULT_CLIENT_INFO,
         )
@@ -364,7 +440,7 @@ def test_list_voices(transport: str = "grpc", request_type=cloud_tts.ListVoicesR
     request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(type(client._transport.list_voices), "__call__") as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -377,6 +453,7 @@ def test_list_voices(transport: str = "grpc", request_type=cloud_tts.ListVoicesR
         assert args[0] == cloud_tts.ListVoicesRequest()
 
     # Establish that the response is the type that we expect.
+
     assert isinstance(response, cloud_tts.ListVoicesResponse)
 
 
@@ -384,20 +461,36 @@ def test_list_voices_from_dict():
     test_list_voices(request_type=dict)
 
 
+def test_list_voices_empty_call():
+    # This test is a coverage failsafe to make sure that totally empty calls,
+    # i.e. request == None and no flattened fields passed, work.
+    client = TextToSpeechClient(
+        credentials=credentials.AnonymousCredentials(), transport="grpc",
+    )
+
+    # Mock the actual call within the gRPC stub, and fake the request.
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
+        client.list_voices()
+        call.assert_called()
+        _, args, _ = call.mock_calls[0]
+
+        assert args[0] == cloud_tts.ListVoicesRequest()
+
+
 @pytest.mark.asyncio
-async def test_list_voices_async(transport: str = "grpc_asyncio"):
+async def test_list_voices_async(
+    transport: str = "grpc_asyncio", request_type=cloud_tts.ListVoicesRequest
+):
     client = TextToSpeechAsyncClient(
         credentials=credentials.AnonymousCredentials(), transport=transport,
     )
 
     # Everything is optional in proto3 as far as the runtime is concerned,
     # and we are mocking out the actual API, so just send an empty request.
-    request = cloud_tts.ListVoicesRequest()
+    request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(
-        type(client._client._transport.list_voices), "__call__"
-    ) as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(
             cloud_tts.ListVoicesResponse()
@@ -409,17 +502,22 @@ async def test_list_voices_async(transport: str = "grpc_asyncio"):
         assert len(call.mock_calls)
         _, args, _ = call.mock_calls[0]
 
-        assert args[0] == request
+        assert args[0] == cloud_tts.ListVoicesRequest()
 
     # Establish that the response is the type that we expect.
     assert isinstance(response, cloud_tts.ListVoicesResponse)
 
 
+@pytest.mark.asyncio
+async def test_list_voices_async_from_dict():
+    await test_list_voices_async(request_type=dict)
+
+
 def test_list_voices_flattened():
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(type(client._transport.list_voices), "__call__") as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -451,9 +549,7 @@ async def test_list_voices_flattened_async():
     client = TextToSpeechAsyncClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
-    with mock.patch.object(
-        type(client._client._transport.list_voices), "__call__"
-    ) as call:
+    with mock.patch.object(type(client.transport.list_voices), "__call__") as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.ListVoicesResponse()
 
@@ -497,7 +593,7 @@ def test_synthesize_speech(
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse(
@@ -513,6 +609,7 @@ def test_synthesize_speech(
         assert args[0] == cloud_tts.SynthesizeSpeechRequest()
 
     # Establish that the response is the type that we expect.
+
     assert isinstance(response, cloud_tts.SynthesizeSpeechResponse)
 
     assert response.audio_content == b"audio_content_blob"
@@ -522,19 +619,39 @@ def test_synthesize_speech_from_dict():
     test_synthesize_speech(request_type=dict)
 
 
+def test_synthesize_speech_empty_call():
+    # This test is a coverage failsafe to make sure that totally empty calls,
+    # i.e. request == None and no flattened fields passed, work.
+    client = TextToSpeechClient(
+        credentials=credentials.AnonymousCredentials(), transport="grpc",
+    )
+
+    # Mock the actual call within the gRPC stub, and fake the request.
+    with mock.patch.object(
+        type(client.transport.synthesize_speech), "__call__"
+    ) as call:
+        client.synthesize_speech()
+        call.assert_called()
+        _, args, _ = call.mock_calls[0]
+
+        assert args[0] == cloud_tts.SynthesizeSpeechRequest()
+
+
 @pytest.mark.asyncio
-async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
+async def test_synthesize_speech_async(
+    transport: str = "grpc_asyncio", request_type=cloud_tts.SynthesizeSpeechRequest
+):
     client = TextToSpeechAsyncClient(
         credentials=credentials.AnonymousCredentials(), transport=transport,
     )
 
     # Everything is optional in proto3 as far as the runtime is concerned,
     # and we are mocking out the actual API, so just send an empty request.
-    request = cloud_tts.SynthesizeSpeechRequest()
+    request = request_type()
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(
@@ -547,7 +664,7 @@ async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
         assert len(call.mock_calls)
         _, args, _ = call.mock_calls[0]
 
-        assert args[0] == request
+        assert args[0] == cloud_tts.SynthesizeSpeechRequest()
 
     # Establish that the response is the type that we expect.
     assert isinstance(response, cloud_tts.SynthesizeSpeechResponse)
@@ -555,12 +672,17 @@ async def test_synthesize_speech_async(transport: str = "grpc_asyncio"):
     assert response.audio_content == b"audio_content_blob"
 
 
+@pytest.mark.asyncio
+async def test_synthesize_speech_async_from_dict():
+    await test_synthesize_speech_async(request_type=dict)
+
+
 def test_synthesize_speech_flattened():
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse()
@@ -613,7 +735,7 @@ async def test_synthesize_speech_flattened_async():
 
     # Mock the actual call within the gRPC stub, and fake the request.
     with mock.patch.object(
-        type(client._client._transport.synthesize_speech), "__call__"
+        type(client.transport.synthesize_speech), "__call__"
     ) as call:
         # Designate an appropriate return value for the call.
         call.return_value = cloud_tts.SynthesizeSpeechResponse()
@@ -700,7 +822,7 @@ def test_transport_instance():
         credentials=credentials.AnonymousCredentials(),
     )
     client = TextToSpeechClient(transport=transport)
-    assert client._transport is transport
+    assert client.transport is transport
 
 
 def test_transport_get_channel():
@@ -718,10 +840,25 @@ def test_transport_get_channel():
     assert channel
 
 
+@pytest.mark.parametrize(
+    "transport_class",
+    [
+        transports.TextToSpeechGrpcTransport,
+        transports.TextToSpeechGrpcAsyncIOTransport,
+    ],
+)
+def test_transport_adc(transport_class):
+    # Test default credentials are used if not provided.
+    with mock.patch.object(auth, "default") as adc:
+        adc.return_value = (credentials.AnonymousCredentials(), None)
+        transport_class()
+        adc.assert_called_once()
+
+
 def test_transport_grpc_default():
     # A client should use the gRPC transport by default.
     client = TextToSpeechClient(credentials=credentials.AnonymousCredentials(),)
-    assert isinstance(client._transport, transports.TextToSpeechGrpcTransport,)
+    assert isinstance(client.transport, transports.TextToSpeechGrpcTransport,)
 
 
 def test_text_to_speech_base_transport_error():
@@ -773,6 +910,17 @@ def test_text_to_speech_base_transport_with_credentials_file():
         )
 
 
+def test_text_to_speech_base_transport_with_adc():
+    # Test the default credentials are used if credentials and credentials_file are None.
+    with mock.patch.object(auth, "default") as adc, mock.patch(
+        "google.cloud.texttospeech_v1beta1.services.text_to_speech.transports.TextToSpeechTransport._prep_wrapped_messages"
+    ) as Transport:
+        Transport.return_value = None
+        adc.return_value = (credentials.AnonymousCredentials(), None)
+        transport = transports.TextToSpeechTransport()
+        adc.assert_called_once()
+
+
 def test_text_to_speech_auth_adc():
     # If no credentials are provided, we should use ADC credentials.
     with mock.patch.object(auth, "default") as adc:
@@ -798,6 +946,48 @@ def test_text_to_speech_transport_auth_adc():
         )
 
 
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_grpc_transport_client_cert_source_for_mtls(transport_class):
+    cred = credentials.AnonymousCredentials()
+
+    # Check ssl_channel_credentials is used if provided.
+    with mock.patch.object(transport_class, "create_channel") as mock_create_channel:
+        mock_ssl_channel_creds = mock.Mock()
+        transport_class(
+            host="squid.clam.whelk",
+            credentials=cred,
+            ssl_channel_credentials=mock_ssl_channel_creds,
+        )
+        mock_create_channel.assert_called_once_with(
+            "squid.clam.whelk:443",
+            credentials=cred,
+            credentials_file=None,
+            scopes=("https://www.googleapis.com/auth/cloud-platform",),
+            ssl_credentials=mock_ssl_channel_creds,
+            quota_project_id=None,
+            options=[
+                ("grpc.max_send_message_length", -1),
+                ("grpc.max_receive_message_length", -1),
+            ],
+        )
+
+    # Check if ssl_channel_credentials is not provided, then client_cert_source_for_mtls
+    # is used.
+    with mock.patch.object(transport_class, "create_channel", return_value=mock.Mock()):
+        with mock.patch("grpc.ssl_channel_credentials") as mock_ssl_cred:
+            transport_class(
+                credentials=cred,
+                client_cert_source_for_mtls=client_cert_source_callback,
+            )
+            expected_cert, expected_key = client_cert_source_callback()
+            mock_ssl_cred.assert_called_once_with(
+                certificate_chain=expected_cert, private_key=expected_key
+            )
+
+
 def test_text_to_speech_host_no_port():
     client = TextToSpeechClient(
         credentials=credentials.AnonymousCredentials(),
@@ -805,7 +995,7 @@ def test_text_to_speech_host_no_port():
             api_endpoint="texttospeech.googleapis.com"
         ),
     )
-    assert client._transport._host == "texttospeech.googleapis.com:443"
+    assert client.transport._host == "texttospeech.googleapis.com:443"
 
 
 def test_text_to_speech_host_with_port():
@@ -815,185 +1005,224 @@ def test_text_to_speech_host_with_port():
             api_endpoint="texttospeech.googleapis.com:8000"
         ),
     )
-    assert client._transport._host == "texttospeech.googleapis.com:8000"
+    assert client.transport._host == "texttospeech.googleapis.com:8000"
 
 
 def test_text_to_speech_grpc_transport_channel():
-    channel = grpc.insecure_channel("http://localhost/")
+    channel = grpc.secure_channel("http://localhost/", grpc.local_channel_credentials())
 
-    # Check that if channel is provided, mtls endpoint and client_cert_source
-    # won't be used.
-    callback = mock.MagicMock()
+    # Check that channel is used if provided.
     transport = transports.TextToSpeechGrpcTransport(
-        host="squid.clam.whelk",
-        channel=channel,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=callback,
+        host="squid.clam.whelk", channel=channel,
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
-    assert not callback.called
+    assert transport._ssl_channel_credentials == None
 
 
 def test_text_to_speech_grpc_asyncio_transport_channel():
-    channel = aio.insecure_channel("http://localhost/")
+    channel = aio.secure_channel("http://localhost/", grpc.local_channel_credentials())
 
-    # Check that if channel is provided, mtls endpoint and client_cert_source
-    # won't be used.
-    callback = mock.MagicMock()
+    # Check that channel is used if provided.
     transport = transports.TextToSpeechGrpcAsyncIOTransport(
-        host="squid.clam.whelk",
-        channel=channel,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=callback,
+        host="squid.clam.whelk", channel=channel,
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
-    assert not callback.called
+    assert transport._ssl_channel_credentials == None
 
 
-@mock.patch("grpc.ssl_channel_credentials", autospec=True)
-@mock.patch("google.api_core.grpc_helpers.create_channel", autospec=True)
-def test_text_to_speech_grpc_transport_channel_mtls_with_client_cert_source(
-    grpc_create_channel, grpc_ssl_channel_cred
-):
-    # Check that if channel is None, but api_mtls_endpoint and client_cert_source
-    # are provided, then a mTLS channel will be created.
-    mock_cred = mock.Mock()
+# Remove this test when deprecated arguments (api_mtls_endpoint, client_cert_source) are
+# removed from grpc/grpc_asyncio transport constructor.
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_transport_channel_mtls_with_client_cert_source(transport_class):
+    with mock.patch(
+        "grpc.ssl_channel_credentials", autospec=True
+    ) as grpc_ssl_channel_cred:
+        with mock.patch.object(
+            transport_class, "create_channel"
+        ) as grpc_create_channel:
+            mock_ssl_cred = mock.Mock()
+            grpc_ssl_channel_cred.return_value = mock_ssl_cred
+
+            mock_grpc_channel = mock.Mock()
+            grpc_create_channel.return_value = mock_grpc_channel
+
+            cred = credentials.AnonymousCredentials()
+            with pytest.warns(DeprecationWarning):
+                with mock.patch.object(auth, "default") as adc:
+                    adc.return_value = (cred, None)
+                    transport = transport_class(
+                        host="squid.clam.whelk",
+                        api_mtls_endpoint="mtls.squid.clam.whelk",
+                        client_cert_source=client_cert_source_callback,
+                    )
+                    adc.assert_called_once()
+
+            grpc_ssl_channel_cred.assert_called_once_with(
+                certificate_chain=b"cert bytes", private_key=b"key bytes"
+            )
+            grpc_create_channel.assert_called_once_with(
+                "mtls.squid.clam.whelk:443",
+                credentials=cred,
+                credentials_file=None,
+                scopes=("https://www.googleapis.com/auth/cloud-platform",),
+                ssl_credentials=mock_ssl_cred,
+                quota_project_id=None,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            assert transport.grpc_channel == mock_grpc_channel
+            assert transport._ssl_channel_credentials == mock_ssl_cred
+
 
+# Remove this test when deprecated arguments (api_mtls_endpoint, client_cert_source) are
+# removed from grpc/grpc_asyncio transport constructor.
+@pytest.mark.parametrize(
+    "transport_class",
+    [transports.TextToSpeechGrpcTransport, transports.TextToSpeechGrpcAsyncIOTransport],
+)
+def test_text_to_speech_transport_channel_mtls_with_adc(transport_class):
     mock_ssl_cred = mock.Mock()
-    grpc_ssl_channel_cred.return_value = mock_ssl_cred
+    with mock.patch.multiple(
+        "google.auth.transport.grpc.SslCredentials",
+        __init__=mock.Mock(return_value=None),
+        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
+    ):
+        with mock.patch.object(
+            transport_class, "create_channel"
+        ) as grpc_create_channel:
+            mock_grpc_channel = mock.Mock()
+            grpc_create_channel.return_value = mock_grpc_channel
+            mock_cred = mock.Mock()
+
+            with pytest.warns(DeprecationWarning):
+                transport = transport_class(
+                    host="squid.clam.whelk",
+                    credentials=mock_cred,
+                    api_mtls_endpoint="mtls.squid.clam.whelk",
+                    client_cert_source=None,
+                )
 
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
+            grpc_create_channel.assert_called_once_with(
+                "mtls.squid.clam.whelk:443",
+                credentials=mock_cred,
+                credentials_file=None,
+                scopes=("https://www.googleapis.com/auth/cloud-platform",),
+                ssl_credentials=mock_ssl_cred,
+                quota_project_id=None,
+                options=[
+                    ("grpc.max_send_message_length", -1),
+                    ("grpc.max_receive_message_length", -1),
+                ],
+            )
+            assert transport.grpc_channel == mock_grpc_channel
 
-    transport = transports.TextToSpeechGrpcTransport(
-        host="squid.clam.whelk",
-        credentials=mock_cred,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=client_cert_source_callback,
-    )
-    grpc_ssl_channel_cred.assert_called_once_with(
-        certificate_chain=b"cert bytes", private_key=b"key bytes"
-    )
-    grpc_create_channel.assert_called_once_with(
-        "mtls.squid.clam.whelk:443",
-        credentials=mock_cred,
-        credentials_file=None,
-        scopes=("https://www.googleapis.com/auth/cloud-platform",),
-        ssl_credentials=mock_ssl_cred,
-        quota_project_id=None,
+
+def test_common_billing_account_path():
+    billing_account = "squid"
+
+    expected = "billingAccounts/{billing_account}".format(
+        billing_account=billing_account,
     )
-    assert transport.grpc_channel == mock_grpc_channel
+    actual = TextToSpeechClient.common_billing_account_path(billing_account)
+    assert expected == actual
 
 
-@mock.patch("grpc.ssl_channel_credentials", autospec=True)
-@mock.patch("google.api_core.grpc_helpers_async.create_channel", autospec=True)
-def test_text_to_speech_grpc_asyncio_transport_channel_mtls_with_client_cert_source(
-    grpc_create_channel, grpc_ssl_channel_cred
-):
-    # Check that if channel is None, but api_mtls_endpoint and client_cert_source
-    # are provided, then a mTLS channel will be created.
-    mock_cred = mock.Mock()
+def test_parse_common_billing_account_path():
+    expected = {
+        "billing_account": "clam",
+    }
+    path = TextToSpeechClient.common_billing_account_path(**expected)
 
-    mock_ssl_cred = mock.Mock()
-    grpc_ssl_channel_cred.return_value = mock_ssl_cred
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_billing_account_path(path)
+    assert expected == actual
 
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    transport = transports.TextToSpeechGrpcAsyncIOTransport(
-        host="squid.clam.whelk",
-        credentials=mock_cred,
-        api_mtls_endpoint="mtls.squid.clam.whelk",
-        client_cert_source=client_cert_source_callback,
-    )
-    grpc_ssl_channel_cred.assert_called_once_with(
-        certificate_chain=b"cert bytes", private_key=b"key bytes"
-    )
-    grpc_create_channel.assert_called_once_with(
-        "mtls.squid.clam.whelk:443",
-        credentials=mock_cred,
-        credentials_file=None,
-        scopes=("https://www.googleapis.com/auth/cloud-platform",),
-        ssl_credentials=mock_ssl_cred,
-        quota_project_id=None,
-    )
-    assert transport.grpc_channel == mock_grpc_channel
+def test_common_folder_path():
+    folder = "whelk"
 
+    expected = "folders/{folder}".format(folder=folder,)
+    actual = TextToSpeechClient.common_folder_path(folder)
+    assert expected == actual
 
-@pytest.mark.parametrize(
-    "api_mtls_endpoint", ["mtls.squid.clam.whelk", "mtls.squid.clam.whelk:443"]
-)
-@mock.patch("google.api_core.grpc_helpers.create_channel", autospec=True)
-def test_text_to_speech_grpc_transport_channel_mtls_with_adc(
-    grpc_create_channel, api_mtls_endpoint
-):
-    # Check that if channel and client_cert_source are None, but api_mtls_endpoint
-    # is provided, then a mTLS channel will be created with SSL ADC.
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    # Mock google.auth.transport.grpc.SslCredentials class.
-    mock_ssl_cred = mock.Mock()
-    with mock.patch.multiple(
-        "google.auth.transport.grpc.SslCredentials",
-        __init__=mock.Mock(return_value=None),
-        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
-    ):
-        mock_cred = mock.Mock()
-        transport = transports.TextToSpeechGrpcTransport(
-            host="squid.clam.whelk",
-            credentials=mock_cred,
-            api_mtls_endpoint=api_mtls_endpoint,
-            client_cert_source=None,
-        )
-        grpc_create_channel.assert_called_once_with(
-            "mtls.squid.clam.whelk:443",
-            credentials=mock_cred,
-            credentials_file=None,
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            ssl_credentials=mock_ssl_cred,
-            quota_project_id=None,
-        )
-        assert transport.grpc_channel == mock_grpc_channel
+def test_parse_common_folder_path():
+    expected = {
+        "folder": "octopus",
+    }
+    path = TextToSpeechClient.common_folder_path(**expected)
 
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_folder_path(path)
+    assert expected == actual
 
-@pytest.mark.parametrize(
-    "api_mtls_endpoint", ["mtls.squid.clam.whelk", "mtls.squid.clam.whelk:443"]
-)
-@mock.patch("google.api_core.grpc_helpers_async.create_channel", autospec=True)
-def test_text_to_speech_grpc_asyncio_transport_channel_mtls_with_adc(
-    grpc_create_channel, api_mtls_endpoint
-):
-    # Check that if channel and client_cert_source are None, but api_mtls_endpoint
-    # is provided, then a mTLS channel will be created with SSL ADC.
-    mock_grpc_channel = mock.Mock()
-    grpc_create_channel.return_value = mock_grpc_channel
 
-    # Mock google.auth.transport.grpc.SslCredentials class.
-    mock_ssl_cred = mock.Mock()
-    with mock.patch.multiple(
-        "google.auth.transport.grpc.SslCredentials",
-        __init__=mock.Mock(return_value=None),
-        ssl_credentials=mock.PropertyMock(return_value=mock_ssl_cred),
-    ):
-        mock_cred = mock.Mock()
-        transport = transports.TextToSpeechGrpcAsyncIOTransport(
-            host="squid.clam.whelk",
-            credentials=mock_cred,
-            api_mtls_endpoint=api_mtls_endpoint,
-            client_cert_source=None,
-        )
-        grpc_create_channel.assert_called_once_with(
-            "mtls.squid.clam.whelk:443",
-            credentials=mock_cred,
-            credentials_file=None,
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            ssl_credentials=mock_ssl_cred,
-            quota_project_id=None,
-        )
-        assert transport.grpc_channel == mock_grpc_channel
+def test_common_organization_path():
+    organization = "oyster"
+
+    expected = "organizations/{organization}".format(organization=organization,)
+    actual = TextToSpeechClient.common_organization_path(organization)
+    assert expected == actual
+
+
+def test_parse_common_organization_path():
+    expected = {
+        "organization": "nudibranch",
+    }
+    path = TextToSpeechClient.common_organization_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_organization_path(path)
+    assert expected == actual
+
+
+def test_common_project_path():
+    project = "cuttlefish"
+
+    expected = "projects/{project}".format(project=project,)
+    actual = TextToSpeechClient.common_project_path(project)
+    assert expected == actual
+
+
+def test_parse_common_project_path():
+    expected = {
+        "project": "mussel",
+    }
+    path = TextToSpeechClient.common_project_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_project_path(path)
+    assert expected == actual
+
+
+def test_common_location_path():
+    project = "winkle"
+    location = "nautilus"
+
+    expected = "projects/{project}/locations/{location}".format(
+        project=project, location=location,
+    )
+    actual = TextToSpeechClient.common_location_path(project, location)
+    assert expected == actual
+
+
+def test_parse_common_location_path():
+    expected = {
+        "project": "scallop",
+        "location": "abalone",
+    }
+    path = TextToSpeechClient.common_location_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = TextToSpeechClient.parse_common_location_path(path)
+    assert expected == actual
 
 
 def test_client_withDEFAULT_CLIENT_INFO():