diff --git a/google/cloud/domains_v1/services/domains/async_client.py b/google/cloud/domains_v1/services/domains/async_client.py
index 9a293f0..f746bd0 100644
--- a/google/cloud/domains_v1/services/domains/async_client.py
+++ b/google/cloud/domains_v1/services/domains/async_client.py
@@ -19,13 +19,15 @@
 from typing import Dict, Sequence, Tuple, Type, Union
 import pkg_resources
 
-import google.api_core.client_options as ClientOptions  # type: ignore
+from google.api_core.client_options import ClientOptions  # type: ignore
 from google.api_core import exceptions as core_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 as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
+OptionalRetry = Union[retries.Retry, object]
+
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
 from google.cloud.domains_v1.services.domains import pagers
@@ -163,11 +165,11 @@ def __init__(
 
     async def search_domains(
         self,
-        request: domains.SearchDomainsRequest = None,
+        request: Union[domains.SearchDomainsRequest, dict] = None,
         *,
         location: str = None,
         query: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.SearchDomainsResponse:
@@ -179,7 +181,7 @@ async def search_domains(
         confirm availability.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.SearchDomainsRequest`):
+            request (Union[google.cloud.domains_v1.types.SearchDomainsRequest, dict]):
                 The request object. Request for the `SearchDomains`
                 method.
             location (:class:`str`):
@@ -247,11 +249,11 @@ async def search_domains(
 
     async def retrieve_register_parameters(
         self,
-        request: domains.RetrieveRegisterParametersRequest = None,
+        request: Union[domains.RetrieveRegisterParametersRequest, dict] = None,
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveRegisterParametersResponse:
@@ -260,7 +262,7 @@ async def retrieve_register_parameters(
         call ``RegisterDomain``.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.RetrieveRegisterParametersRequest`):
+            request (Union[google.cloud.domains_v1.types.RetrieveRegisterParametersRequest, dict]):
                 The request object. Request for the
                 `RetrieveRegisterParameters` method.
             location (:class:`str`):
@@ -329,12 +331,12 @@ async def retrieve_register_parameters(
 
     async def register_domain(
         self,
-        request: domains.RegisterDomainRequest = None,
+        request: Union[domains.RegisterDomainRequest, dict] = None,
         *,
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -354,7 +356,7 @@ async def register_domain(
         and retry registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.RegisterDomainRequest`):
+            request (Union[google.cloud.domains_v1.types.RegisterDomainRequest, dict]):
                 The request object. Request for the `RegisterDomain`
                 method.
             parent (:class:`str`):
@@ -466,11 +468,11 @@ async def register_domain(
 
     async def retrieve_transfer_parameters(
         self,
-        request: domains.RetrieveTransferParametersRequest = None,
+        request: Union[domains.RetrieveTransferParametersRequest, dict] = None,
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveTransferParametersResponse:
@@ -481,7 +483,7 @@ async def retrieve_transfer_parameters(
         Use the returned values to call ``TransferDomain``.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.RetrieveTransferParametersRequest`):
+            request (Union[google.cloud.domains_v1.types.RetrieveTransferParametersRequest, dict]):
                 The request object. Request for the
                 `RetrieveTransferParameters` method.
             location (:class:`str`):
@@ -550,13 +552,13 @@ async def retrieve_transfer_parameters(
 
     async def transfer_domain(
         self,
-        request: domains.TransferDomainRequest = None,
+        request: Union[domains.TransferDomainRequest, dict] = None,
         *,
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
         authorization_code: domains.AuthorizationCode = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -586,7 +588,7 @@ async def transfer_domain(
         the resource and retry the transfer.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.TransferDomainRequest`):
+            request (Union[google.cloud.domains_v1.types.TransferDomainRequest, dict]):
                 The request object. Request for the `TransferDomain`
                 method.
             parent (:class:`str`):
@@ -716,17 +718,17 @@ async def transfer_domain(
 
     async def list_registrations(
         self,
-        request: domains.ListRegistrationsRequest = None,
+        request: Union[domains.ListRegistrationsRequest, dict] = None,
         *,
         parent: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> pagers.ListRegistrationsAsyncPager:
         r"""Lists the ``Registration`` resources in a project.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ListRegistrationsRequest`):
+            request (Union[google.cloud.domains_v1.types.ListRegistrationsRequest, dict]):
                 The request object. Request for the `ListRegistrations`
                 method.
             parent (:class:`str`):
@@ -796,17 +798,17 @@ async def list_registrations(
 
     async def get_registration(
         self,
-        request: domains.GetRegistrationRequest = None,
+        request: Union[domains.GetRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.Registration:
         r"""Gets the details of a ``Registration`` resource.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.GetRegistrationRequest`):
+            request (Union[google.cloud.domains_v1.types.GetRegistrationRequest, dict]):
                 The request object. Request for the `GetRegistration`
                 method.
             name (:class:`str`):
@@ -887,11 +889,11 @@ async def get_registration(
 
     async def update_registration(
         self,
-        request: domains.UpdateRegistrationRequest = None,
+        request: Union[domains.UpdateRegistrationRequest, dict] = None,
         *,
         registration: domains.Registration = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -906,7 +908,7 @@ async def update_registration(
            ``ConfigureContactSettings``
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.UpdateRegistrationRequest`):
+            request (Union[google.cloud.domains_v1.types.UpdateRegistrationRequest, dict]):
                 The request object. Request for the `UpdateRegistration`
                 method.
             registration (:class:`google.cloud.domains_v1.types.Registration`):
@@ -1008,19 +1010,19 @@ async def update_registration(
 
     async def configure_management_settings(
         self,
-        request: domains.ConfigureManagementSettingsRequest = None,
+        request: Union[domains.ConfigureManagementSettingsRequest, dict] = None,
         *,
         registration: str = None,
         management_settings: domains.ManagementSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
         r"""Updates a ``Registration``'s management settings.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ConfigureManagementSettingsRequest`):
+            request (Union[google.cloud.domains_v1.types.ConfigureManagementSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureManagementSettings` method.
             registration (:class:`str`):
@@ -1132,19 +1134,19 @@ async def configure_management_settings(
 
     async def configure_dns_settings(
         self,
-        request: domains.ConfigureDnsSettingsRequest = None,
+        request: Union[domains.ConfigureDnsSettingsRequest, dict] = None,
         *,
         registration: str = None,
         dns_settings: domains.DnsSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
         r"""Updates a ``Registration``'s DNS settings.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ConfigureDnsSettingsRequest`):
+            request (Union[google.cloud.domains_v1.types.ConfigureDnsSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureDnsSettings` method.
             registration (:class:`str`):
@@ -1263,12 +1265,12 @@ async def configure_dns_settings(
 
     async def configure_contact_settings(
         self,
-        request: domains.ConfigureContactSettingsRequest = None,
+        request: Union[domains.ConfigureContactSettingsRequest, dict] = None,
         *,
         registration: str = None,
         contact_settings: domains.ContactSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1276,7 +1278,7 @@ async def configure_contact_settings(
         require confirmation by the domain's registrant contact .
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ConfigureContactSettingsRequest`):
+            request (Union[google.cloud.domains_v1.types.ConfigureContactSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureContactSettings` method.
             registration (:class:`str`):
@@ -1388,10 +1390,10 @@ async def configure_contact_settings(
 
     async def export_registration(
         self,
-        request: domains.ExportRegistrationRequest = None,
+        request: Union[domains.ExportRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1407,7 +1409,7 @@ async def export_registration(
         sets up billing in Google Domains.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ExportRegistrationRequest`):
+            request (Union[google.cloud.domains_v1.types.ExportRegistrationRequest, dict]):
                 The request object. Request for the `ExportRegistration`
                 method.
             name (:class:`str`):
@@ -1498,10 +1500,10 @@ async def export_registration(
 
     async def delete_registration(
         self,
-        request: domains.DeleteRegistrationRequest = None,
+        request: Union[domains.DeleteRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1529,7 +1531,7 @@ async def delete_registration(
         sets up billing in Google Domains.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.DeleteRegistrationRequest`):
+            request (Union[google.cloud.domains_v1.types.DeleteRegistrationRequest, dict]):
                 The request object. Request for the `DeleteRegistration`
                 method.
             name (:class:`str`):
@@ -1611,10 +1613,10 @@ async def delete_registration(
 
     async def retrieve_authorization_code(
         self,
-        request: domains.RetrieveAuthorizationCodeRequest = None,
+        request: Union[domains.RetrieveAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1625,7 +1627,7 @@ async def retrieve_authorization_code(
         the initial domain registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.RetrieveAuthorizationCodeRequest`):
+            request (Union[google.cloud.domains_v1.types.RetrieveAuthorizationCodeRequest, dict]):
                 The request object. Request for the
                 `RetrieveAuthorizationCode` method.
             registration (:class:`str`):
@@ -1687,10 +1689,10 @@ async def retrieve_authorization_code(
 
     async def reset_authorization_code(
         self,
-        request: domains.ResetAuthorizationCodeRequest = None,
+        request: Union[domains.ResetAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1701,7 +1703,7 @@ async def reset_authorization_code(
         the initial domain registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1.types.ResetAuthorizationCodeRequest`):
+            request (Union[google.cloud.domains_v1.types.ResetAuthorizationCodeRequest, dict]):
                 The request object. Request for the
                 `ResetAuthorizationCode` method.
             registration (:class:`str`):
diff --git a/google/cloud/domains_v1/services/domains/client.py b/google/cloud/domains_v1/services/domains/client.py
index 6774df5..b7727a8 100644
--- a/google/cloud/domains_v1/services/domains/client.py
+++ b/google/cloud/domains_v1/services/domains/client.py
@@ -30,6 +30,8 @@
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
+OptionalRetry = Union[retries.Retry, object]
+
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
 from google.cloud.domains_v1.services.domains import pagers
@@ -359,7 +361,7 @@ def search_domains(
         *,
         location: str = None,
         query: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.SearchDomainsResponse:
@@ -443,7 +445,7 @@ def retrieve_register_parameters(
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveRegisterParametersResponse:
@@ -528,7 +530,7 @@ def register_domain(
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -664,7 +666,7 @@ def retrieve_transfer_parameters(
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveTransferParametersResponse:
@@ -752,7 +754,7 @@ def transfer_domain(
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
         authorization_code: domains.AuthorizationCode = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -915,7 +917,7 @@ def list_registrations(
         request: Union[domains.ListRegistrationsRequest, dict] = None,
         *,
         parent: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> pagers.ListRegistrationsPager:
@@ -995,7 +997,7 @@ def get_registration(
         request: Union[domains.GetRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.Registration:
@@ -1087,7 +1089,7 @@ def update_registration(
         *,
         registration: domains.Registration = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1209,7 +1211,7 @@ def configure_management_settings(
         registration: str = None,
         management_settings: domains.ManagementSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1335,7 +1337,7 @@ def configure_dns_settings(
         registration: str = None,
         dns_settings: domains.DnsSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1466,7 +1468,7 @@ def configure_contact_settings(
         registration: str = None,
         contact_settings: domains.ContactSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1591,7 +1593,7 @@ def export_registration(
         request: Union[domains.ExportRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1701,7 +1703,7 @@ def delete_registration(
         request: Union[domains.DeleteRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1814,7 +1816,7 @@ def retrieve_authorization_code(
         request: Union[domains.RetrieveAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1892,7 +1894,7 @@ def reset_authorization_code(
         request: Union[domains.ResetAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
diff --git a/google/cloud/domains_v1/services/domains/transports/base.py b/google/cloud/domains_v1/services/domains/transports/base.py
index 522654d..4d8b6a6 100644
--- a/google/cloud/domains_v1/services/domains/transports/base.py
+++ b/google/cloud/domains_v1/services/domains/transports/base.py
@@ -15,7 +15,6 @@
 #
 import abc
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Union
-import packaging.version
 import pkg_resources
 
 import google.auth  # type: ignore
@@ -37,15 +36,6 @@
 except pkg_resources.DistributionNotFound:
     DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo()
 
-try:
-    # google.auth.__version__ was added in 1.26.0
-    _GOOGLE_AUTH_VERSION = google.auth.__version__
-except AttributeError:
-    try:  # try pkg_resources if it is available
-        _GOOGLE_AUTH_VERSION = pkg_resources.get_distribution("google-auth").version
-    except pkg_resources.DistributionNotFound:  # pragma: NO COVER
-        _GOOGLE_AUTH_VERSION = None
-
 
 class DomainsTransport(abc.ABC):
     """Abstract transport class for Domains."""
@@ -95,7 +85,7 @@ def __init__(
             host += ":443"
         self._host = host
 
-        scopes_kwargs = self._get_scopes_kwargs(self._host, scopes)
+        scopes_kwargs = {"scopes": scopes, "default_scopes": self.AUTH_SCOPES}
 
         # Save the scopes.
         self._scopes = scopes
@@ -128,29 +118,6 @@ def __init__(
         # Save the credentials.
         self._credentials = credentials
 
-    # TODO(busunkim): This method is in the base transport
-    # to avoid duplicating code across the transport classes. These functions
-    # should be deleted once the minimum required versions of google-auth is increased.
-
-    # TODO: Remove this function once google-auth >= 1.25.0 is required
-    @classmethod
-    def _get_scopes_kwargs(
-        cls, host: str, scopes: Optional[Sequence[str]]
-    ) -> Dict[str, Optional[Sequence[str]]]:
-        """Returns scopes kwargs to pass to google-auth methods depending on the google-auth version"""
-
-        scopes_kwargs = {}
-
-        if _GOOGLE_AUTH_VERSION and (
-            packaging.version.parse(_GOOGLE_AUTH_VERSION)
-            >= packaging.version.parse("1.25.0")
-        ):
-            scopes_kwargs = {"scopes": scopes, "default_scopes": cls.AUTH_SCOPES}
-        else:
-            scopes_kwargs = {"scopes": scopes or cls.AUTH_SCOPES}
-
-        return scopes_kwargs
-
     def _prep_wrapped_messages(self, client_info):
         # Precompute the wrapped methods.
         self._wrapped_methods = {
@@ -225,7 +192,7 @@ def close(self):
         raise NotImplementedError()
 
     @property
-    def operations_client(self) -> operations_v1.OperationsClient:
+    def operations_client(self):
         """Return the client designed to process long-running operations."""
         raise NotImplementedError()
 
diff --git a/google/cloud/domains_v1/services/domains/transports/grpc.py b/google/cloud/domains_v1/services/domains/transports/grpc.py
index d4c7f2d..fc80444 100644
--- a/google/cloud/domains_v1/services/domains/transports/grpc.py
+++ b/google/cloud/domains_v1/services/domains/transports/grpc.py
@@ -113,7 +113,7 @@ def __init__(
         self._grpc_channel = None
         self._ssl_channel_credentials = ssl_channel_credentials
         self._stubs: Dict[str, Callable] = {}
-        self._operations_client = None
+        self._operations_client: Optional[operations_v1.OperationsClient] = None
 
         if api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
diff --git a/google/cloud/domains_v1/services/domains/transports/grpc_asyncio.py b/google/cloud/domains_v1/services/domains/transports/grpc_asyncio.py
index 50c2521..aa52fa8 100644
--- a/google/cloud/domains_v1/services/domains/transports/grpc_asyncio.py
+++ b/google/cloud/domains_v1/services/domains/transports/grpc_asyncio.py
@@ -21,7 +21,6 @@
 from google.api_core import operations_v1  # type: ignore
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
-import packaging.version
 
 import grpc  # type: ignore
 from grpc.experimental import aio  # type: ignore
@@ -160,7 +159,7 @@ def __init__(
         self._grpc_channel = None
         self._ssl_channel_credentials = ssl_channel_credentials
         self._stubs: Dict[str, Callable] = {}
-        self._operations_client = None
+        self._operations_client: Optional[operations_v1.OperationsAsyncClient] = None
 
         if api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
diff --git a/google/cloud/domains_v1/types/domains.py b/google/cloud/domains_v1/types/domains.py
index 266855f..72242a2 100644
--- a/google/cloud/domains_v1/types/domains.py
+++ b/google/cloud/domains_v1/types/domains.py
@@ -231,13 +231,22 @@ class DnsSettings(proto.Message):
     r"""Defines the DNS configuration of a ``Registration``, including name
     servers, DNSSEC, and glue records.
 
+    This message has `oneof`_ fields (mutually exclusive fields).
+    For each oneof, at most one member field can be set at the same time.
+    Setting any member of the oneof automatically clears all other
+    members.
+
+    .. _oneof: https://proto-plus-python.readthedocs.io/en/stable/fields.html#oneofs-mutually-exclusive-fields
+
     Attributes:
         custom_dns (google.cloud.domains_v1.types.DnsSettings.CustomDns):
             An arbitrary DNS provider identified by its
             name servers.
+            This field is a member of `oneof`_ ``dns_provider``.
         google_domains_dns (google.cloud.domains_v1.types.DnsSettings.GoogleDomainsDns):
             The free DNS zone provided by `Google
             Domains <https://domains.google/>`__.
+            This field is a member of `oneof`_ ``dns_provider``.
         glue_records (Sequence[google.cloud.domains_v1.types.DnsSettings.GlueRecord]):
             The list of glue records for this ``Registration``. Commonly
             empty.
diff --git a/google/cloud/domains_v1beta1/services/domains/async_client.py b/google/cloud/domains_v1beta1/services/domains/async_client.py
index 4deada9..5552879 100644
--- a/google/cloud/domains_v1beta1/services/domains/async_client.py
+++ b/google/cloud/domains_v1beta1/services/domains/async_client.py
@@ -19,13 +19,15 @@
 from typing import Dict, Sequence, Tuple, Type, Union
 import pkg_resources
 
-import google.api_core.client_options as ClientOptions  # type: ignore
+from google.api_core.client_options import ClientOptions  # type: ignore
 from google.api_core import exceptions as core_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 as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
+OptionalRetry = Union[retries.Retry, object]
+
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
 from google.cloud.domains_v1beta1.services.domains import pagers
@@ -163,11 +165,11 @@ def __init__(
 
     async def search_domains(
         self,
-        request: domains.SearchDomainsRequest = None,
+        request: Union[domains.SearchDomainsRequest, dict] = None,
         *,
         location: str = None,
         query: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.SearchDomainsResponse:
@@ -179,7 +181,7 @@ async def search_domains(
         confirm availability.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.SearchDomainsRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.SearchDomainsRequest, dict]):
                 The request object. Request for the `SearchDomains`
                 method.
             location (:class:`str`):
@@ -247,11 +249,11 @@ async def search_domains(
 
     async def retrieve_register_parameters(
         self,
-        request: domains.RetrieveRegisterParametersRequest = None,
+        request: Union[domains.RetrieveRegisterParametersRequest, dict] = None,
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveRegisterParametersResponse:
@@ -260,7 +262,7 @@ async def retrieve_register_parameters(
         call ``RegisterDomain``.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.RetrieveRegisterParametersRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.RetrieveRegisterParametersRequest, dict]):
                 The request object. Request for the
                 `RetrieveRegisterParameters` method.
             location (:class:`str`):
@@ -329,12 +331,12 @@ async def retrieve_register_parameters(
 
     async def register_domain(
         self,
-        request: domains.RegisterDomainRequest = None,
+        request: Union[domains.RegisterDomainRequest, dict] = None,
         *,
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -354,7 +356,7 @@ async def register_domain(
         and retry registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.RegisterDomainRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.RegisterDomainRequest, dict]):
                 The request object. Request for the `RegisterDomain`
                 method.
             parent (:class:`str`):
@@ -466,11 +468,11 @@ async def register_domain(
 
     async def retrieve_transfer_parameters(
         self,
-        request: domains.RetrieveTransferParametersRequest = None,
+        request: Union[domains.RetrieveTransferParametersRequest, dict] = None,
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveTransferParametersResponse:
@@ -481,7 +483,7 @@ async def retrieve_transfer_parameters(
         Use the returned values to call ``TransferDomain``.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.RetrieveTransferParametersRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.RetrieveTransferParametersRequest, dict]):
                 The request object. Request for the
                 `RetrieveTransferParameters` method.
             location (:class:`str`):
@@ -550,13 +552,13 @@ async def retrieve_transfer_parameters(
 
     async def transfer_domain(
         self,
-        request: domains.TransferDomainRequest = None,
+        request: Union[domains.TransferDomainRequest, dict] = None,
         *,
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
         authorization_code: domains.AuthorizationCode = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -586,7 +588,7 @@ async def transfer_domain(
         the resource and retry the transfer.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.TransferDomainRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.TransferDomainRequest, dict]):
                 The request object. Request for the `TransferDomain`
                 method.
             parent (:class:`str`):
@@ -716,17 +718,17 @@ async def transfer_domain(
 
     async def list_registrations(
         self,
-        request: domains.ListRegistrationsRequest = None,
+        request: Union[domains.ListRegistrationsRequest, dict] = None,
         *,
         parent: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> pagers.ListRegistrationsAsyncPager:
         r"""Lists the ``Registration`` resources in a project.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ListRegistrationsRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ListRegistrationsRequest, dict]):
                 The request object. Request for the `ListRegistrations`
                 method.
             parent (:class:`str`):
@@ -796,17 +798,17 @@ async def list_registrations(
 
     async def get_registration(
         self,
-        request: domains.GetRegistrationRequest = None,
+        request: Union[domains.GetRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.Registration:
         r"""Gets the details of a ``Registration`` resource.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.GetRegistrationRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.GetRegistrationRequest, dict]):
                 The request object. Request for the `GetRegistration`
                 method.
             name (:class:`str`):
@@ -887,11 +889,11 @@ async def get_registration(
 
     async def update_registration(
         self,
-        request: domains.UpdateRegistrationRequest = None,
+        request: Union[domains.UpdateRegistrationRequest, dict] = None,
         *,
         registration: domains.Registration = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -906,7 +908,7 @@ async def update_registration(
            ``ConfigureContactSettings``
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.UpdateRegistrationRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.UpdateRegistrationRequest, dict]):
                 The request object. Request for the `UpdateRegistration`
                 method.
             registration (:class:`google.cloud.domains_v1beta1.types.Registration`):
@@ -1008,19 +1010,19 @@ async def update_registration(
 
     async def configure_management_settings(
         self,
-        request: domains.ConfigureManagementSettingsRequest = None,
+        request: Union[domains.ConfigureManagementSettingsRequest, dict] = None,
         *,
         registration: str = None,
         management_settings: domains.ManagementSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
         r"""Updates a ``Registration``'s management settings.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ConfigureManagementSettingsRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ConfigureManagementSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureManagementSettings` method.
             registration (:class:`str`):
@@ -1132,19 +1134,19 @@ async def configure_management_settings(
 
     async def configure_dns_settings(
         self,
-        request: domains.ConfigureDnsSettingsRequest = None,
+        request: Union[domains.ConfigureDnsSettingsRequest, dict] = None,
         *,
         registration: str = None,
         dns_settings: domains.DnsSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
         r"""Updates a ``Registration``'s DNS settings.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ConfigureDnsSettingsRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ConfigureDnsSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureDnsSettings` method.
             registration (:class:`str`):
@@ -1263,12 +1265,12 @@ async def configure_dns_settings(
 
     async def configure_contact_settings(
         self,
-        request: domains.ConfigureContactSettingsRequest = None,
+        request: Union[domains.ConfigureContactSettingsRequest, dict] = None,
         *,
         registration: str = None,
         contact_settings: domains.ContactSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1276,7 +1278,7 @@ async def configure_contact_settings(
         require confirmation by the domain's registrant contact .
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ConfigureContactSettingsRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ConfigureContactSettingsRequest, dict]):
                 The request object. Request for the
                 `ConfigureContactSettings` method.
             registration (:class:`str`):
@@ -1388,10 +1390,10 @@ async def configure_contact_settings(
 
     async def export_registration(
         self,
-        request: domains.ExportRegistrationRequest = None,
+        request: Union[domains.ExportRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1407,7 +1409,7 @@ async def export_registration(
         sets up billing in Google Domains.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ExportRegistrationRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ExportRegistrationRequest, dict]):
                 The request object. Request for the `ExportRegistration`
                 method.
             name (:class:`str`):
@@ -1498,10 +1500,10 @@ async def export_registration(
 
     async def delete_registration(
         self,
-        request: domains.DeleteRegistrationRequest = None,
+        request: Union[domains.DeleteRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation_async.AsyncOperation:
@@ -1529,7 +1531,7 @@ async def delete_registration(
         sets up billing in Google Domains.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.DeleteRegistrationRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.DeleteRegistrationRequest, dict]):
                 The request object. Request for the `DeleteRegistration`
                 method.
             name (:class:`str`):
@@ -1611,10 +1613,10 @@ async def delete_registration(
 
     async def retrieve_authorization_code(
         self,
-        request: domains.RetrieveAuthorizationCodeRequest = None,
+        request: Union[domains.RetrieveAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1625,7 +1627,7 @@ async def retrieve_authorization_code(
         the initial domain registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.RetrieveAuthorizationCodeRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.RetrieveAuthorizationCodeRequest, dict]):
                 The request object. Request for the
                 `RetrieveAuthorizationCode` method.
             registration (:class:`str`):
@@ -1687,10 +1689,10 @@ async def retrieve_authorization_code(
 
     async def reset_authorization_code(
         self,
-        request: domains.ResetAuthorizationCodeRequest = None,
+        request: Union[domains.ResetAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1701,7 +1703,7 @@ async def reset_authorization_code(
         the initial domain registration.
 
         Args:
-            request (:class:`google.cloud.domains_v1beta1.types.ResetAuthorizationCodeRequest`):
+            request (Union[google.cloud.domains_v1beta1.types.ResetAuthorizationCodeRequest, dict]):
                 The request object. Request for the
                 `ResetAuthorizationCode` method.
             registration (:class:`str`):
diff --git a/google/cloud/domains_v1beta1/services/domains/client.py b/google/cloud/domains_v1beta1/services/domains/client.py
index 182e94e..59a0417 100644
--- a/google/cloud/domains_v1beta1/services/domains/client.py
+++ b/google/cloud/domains_v1beta1/services/domains/client.py
@@ -30,6 +30,8 @@
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
+OptionalRetry = Union[retries.Retry, object]
+
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
 from google.cloud.domains_v1beta1.services.domains import pagers
@@ -359,7 +361,7 @@ def search_domains(
         *,
         location: str = None,
         query: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.SearchDomainsResponse:
@@ -443,7 +445,7 @@ def retrieve_register_parameters(
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveRegisterParametersResponse:
@@ -528,7 +530,7 @@ def register_domain(
         parent: str = None,
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -664,7 +666,7 @@ def retrieve_transfer_parameters(
         *,
         location: str = None,
         domain_name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.RetrieveTransferParametersResponse:
@@ -752,7 +754,7 @@ def transfer_domain(
         registration: domains.Registration = None,
         yearly_price: money_pb2.Money = None,
         authorization_code: domains.AuthorizationCode = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -915,7 +917,7 @@ def list_registrations(
         request: Union[domains.ListRegistrationsRequest, dict] = None,
         *,
         parent: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> pagers.ListRegistrationsPager:
@@ -995,7 +997,7 @@ def get_registration(
         request: Union[domains.GetRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.Registration:
@@ -1087,7 +1089,7 @@ def update_registration(
         *,
         registration: domains.Registration = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1209,7 +1211,7 @@ def configure_management_settings(
         registration: str = None,
         management_settings: domains.ManagementSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1335,7 +1337,7 @@ def configure_dns_settings(
         registration: str = None,
         dns_settings: domains.DnsSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1466,7 +1468,7 @@ def configure_contact_settings(
         registration: str = None,
         contact_settings: domains.ContactSettings = None,
         update_mask: field_mask_pb2.FieldMask = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1591,7 +1593,7 @@ def export_registration(
         request: Union[domains.ExportRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1701,7 +1703,7 @@ def delete_registration(
         request: Union[domains.DeleteRegistrationRequest, dict] = None,
         *,
         name: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> operation.Operation:
@@ -1814,7 +1816,7 @@ def retrieve_authorization_code(
         request: Union[domains.RetrieveAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
@@ -1892,7 +1894,7 @@ def reset_authorization_code(
         request: Union[domains.ResetAuthorizationCodeRequest, dict] = None,
         *,
         registration: str = None,
-        retry: retries.Retry = gapic_v1.method.DEFAULT,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
         timeout: float = None,
         metadata: Sequence[Tuple[str, str]] = (),
     ) -> domains.AuthorizationCode:
diff --git a/google/cloud/domains_v1beta1/services/domains/transports/base.py b/google/cloud/domains_v1beta1/services/domains/transports/base.py
index f95e6f9..3ba6000 100644
--- a/google/cloud/domains_v1beta1/services/domains/transports/base.py
+++ b/google/cloud/domains_v1beta1/services/domains/transports/base.py
@@ -15,7 +15,6 @@
 #
 import abc
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Union
-import packaging.version
 import pkg_resources
 
 import google.auth  # type: ignore
@@ -37,15 +36,6 @@
 except pkg_resources.DistributionNotFound:
     DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo()
 
-try:
-    # google.auth.__version__ was added in 1.26.0
-    _GOOGLE_AUTH_VERSION = google.auth.__version__
-except AttributeError:
-    try:  # try pkg_resources if it is available
-        _GOOGLE_AUTH_VERSION = pkg_resources.get_distribution("google-auth").version
-    except pkg_resources.DistributionNotFound:  # pragma: NO COVER
-        _GOOGLE_AUTH_VERSION = None
-
 
 class DomainsTransport(abc.ABC):
     """Abstract transport class for Domains."""
@@ -95,7 +85,7 @@ def __init__(
             host += ":443"
         self._host = host
 
-        scopes_kwargs = self._get_scopes_kwargs(self._host, scopes)
+        scopes_kwargs = {"scopes": scopes, "default_scopes": self.AUTH_SCOPES}
 
         # Save the scopes.
         self._scopes = scopes
@@ -128,29 +118,6 @@ def __init__(
         # Save the credentials.
         self._credentials = credentials
 
-    # TODO(busunkim): This method is in the base transport
-    # to avoid duplicating code across the transport classes. These functions
-    # should be deleted once the minimum required versions of google-auth is increased.
-
-    # TODO: Remove this function once google-auth >= 1.25.0 is required
-    @classmethod
-    def _get_scopes_kwargs(
-        cls, host: str, scopes: Optional[Sequence[str]]
-    ) -> Dict[str, Optional[Sequence[str]]]:
-        """Returns scopes kwargs to pass to google-auth methods depending on the google-auth version"""
-
-        scopes_kwargs = {}
-
-        if _GOOGLE_AUTH_VERSION and (
-            packaging.version.parse(_GOOGLE_AUTH_VERSION)
-            >= packaging.version.parse("1.25.0")
-        ):
-            scopes_kwargs = {"scopes": scopes, "default_scopes": cls.AUTH_SCOPES}
-        else:
-            scopes_kwargs = {"scopes": scopes or cls.AUTH_SCOPES}
-
-        return scopes_kwargs
-
     def _prep_wrapped_messages(self, client_info):
         # Precompute the wrapped methods.
         self._wrapped_methods = {
@@ -225,7 +192,7 @@ def close(self):
         raise NotImplementedError()
 
     @property
-    def operations_client(self) -> operations_v1.OperationsClient:
+    def operations_client(self):
         """Return the client designed to process long-running operations."""
         raise NotImplementedError()
 
diff --git a/google/cloud/domains_v1beta1/services/domains/transports/grpc.py b/google/cloud/domains_v1beta1/services/domains/transports/grpc.py
index a7b69f1..a8f3c90 100644
--- a/google/cloud/domains_v1beta1/services/domains/transports/grpc.py
+++ b/google/cloud/domains_v1beta1/services/domains/transports/grpc.py
@@ -113,7 +113,7 @@ def __init__(
         self._grpc_channel = None
         self._ssl_channel_credentials = ssl_channel_credentials
         self._stubs: Dict[str, Callable] = {}
-        self._operations_client = None
+        self._operations_client: Optional[operations_v1.OperationsClient] = None
 
         if api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
diff --git a/google/cloud/domains_v1beta1/services/domains/transports/grpc_asyncio.py b/google/cloud/domains_v1beta1/services/domains/transports/grpc_asyncio.py
index dc5afa2..fae581a 100644
--- a/google/cloud/domains_v1beta1/services/domains/transports/grpc_asyncio.py
+++ b/google/cloud/domains_v1beta1/services/domains/transports/grpc_asyncio.py
@@ -21,7 +21,6 @@
 from google.api_core import operations_v1  # type: ignore
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
-import packaging.version
 
 import grpc  # type: ignore
 from grpc.experimental import aio  # type: ignore
@@ -160,7 +159,7 @@ def __init__(
         self._grpc_channel = None
         self._ssl_channel_credentials = ssl_channel_credentials
         self._stubs: Dict[str, Callable] = {}
-        self._operations_client = None
+        self._operations_client: Optional[operations_v1.OperationsAsyncClient] = None
 
         if api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint is deprecated", DeprecationWarning)
diff --git a/google/cloud/domains_v1beta1/types/domains.py b/google/cloud/domains_v1beta1/types/domains.py
index cb78f6c..ef9c829 100644
--- a/google/cloud/domains_v1beta1/types/domains.py
+++ b/google/cloud/domains_v1beta1/types/domains.py
@@ -231,13 +231,22 @@ class DnsSettings(proto.Message):
     r"""Defines the DNS configuration of a ``Registration``, including name
     servers, DNSSEC, and glue records.
 
+    This message has `oneof`_ fields (mutually exclusive fields).
+    For each oneof, at most one member field can be set at the same time.
+    Setting any member of the oneof automatically clears all other
+    members.
+
+    .. _oneof: https://proto-plus-python.readthedocs.io/en/stable/fields.html#oneofs-mutually-exclusive-fields
+
     Attributes:
         custom_dns (google.cloud.domains_v1beta1.types.DnsSettings.CustomDns):
             An arbitrary DNS provider identified by its
             name servers.
+            This field is a member of `oneof`_ ``dns_provider``.
         google_domains_dns (google.cloud.domains_v1beta1.types.DnsSettings.GoogleDomainsDns):
             The free DNS zone provided by `Google
             Domains <https://domains.google/>`__.
+            This field is a member of `oneof`_ ``dns_provider``.
         glue_records (Sequence[google.cloud.domains_v1beta1.types.DnsSettings.GlueRecord]):
             The list of glue records for this ``Registration``. Commonly
             empty.
diff --git a/setup.py b/setup.py
index bc3711f..e01e747 100644
--- a/setup.py
+++ b/setup.py
@@ -46,9 +46,8 @@
         # NOTE: Maintainers, please do not require google-api-core>=2.x.x
         # Until this issue is closed
         # https://github.com/googleapis/google-cloud-python/issues/10566
-        "google-api-core[grpc] >= 1.26.0, <3.0.0dev",
+        "google-api-core[grpc] >= 1.28.0, <3.0.0dev",
         "proto-plus >= 1.15.0",
-        "packaging >= 14.3",
     ),
     python_requires=">=3.6",
     classifiers=[
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index a1b329d..c77c322 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -19,7 +19,5 @@
 #
 # e.g., if setup.py has "foo >= 1.14.0, < 2.0.0dev",
 # Then this file should have foo==1.14.0
-google-api-core==1.26.0
+google-api-core==1.28.0
 proto-plus==1.15.0
-packaging==14.3
-google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 is required through google-api-core
diff --git a/tests/unit/gapic/domains_v1/test_domains.py b/tests/unit/gapic/domains_v1/test_domains.py
index 02c853f..971c9b8 100644
--- a/tests/unit/gapic/domains_v1/test_domains.py
+++ b/tests/unit/gapic/domains_v1/test_domains.py
@@ -15,7 +15,6 @@
 #
 import os
 import mock
-import packaging.version
 
 import grpc
 from grpc.experimental import aio
@@ -39,9 +38,6 @@
 from google.cloud.domains_v1.services.domains import DomainsClient
 from google.cloud.domains_v1.services.domains import pagers
 from google.cloud.domains_v1.services.domains import transports
-from google.cloud.domains_v1.services.domains.transports.base import (
-    _GOOGLE_AUTH_VERSION,
-)
 from google.cloud.domains_v1.types import domains
 from google.longrunning import operations_pb2
 from google.oauth2 import service_account
@@ -52,20 +48,6 @@
 import google.auth
 
 
-# TODO(busunkim): Once google-auth >= 1.25.0 is required transitively
-# through google-api-core:
-# - Delete the auth "less than" test cases
-# - Delete these pytest markers (Make the "greater than or equal to" tests the default).
-requires_google_auth_lt_1_25_0 = pytest.mark.skipif(
-    packaging.version.parse(_GOOGLE_AUTH_VERSION) >= packaging.version.parse("1.25.0"),
-    reason="This test requires google-auth < 1.25.0",
-)
-requires_google_auth_gte_1_25_0 = pytest.mark.skipif(
-    packaging.version.parse(_GOOGLE_AUTH_VERSION) < packaging.version.parse("1.25.0"),
-    reason="This test requires google-auth >= 1.25.0",
-)
-
-
 def client_cert_source_callback():
     return b"cert bytes", b"key bytes"
 
@@ -200,7 +182,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     options = client_options.ClientOptions(api_endpoint="squid.clam.whelk")
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -217,7 +199,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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()
+            client = client_class(transport=transport_name)
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
@@ -234,7 +216,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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()
+            client = client_class(transport=transport_name)
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
@@ -263,7 +245,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -318,7 +300,7 @@ def test_domains_client_mtls_env_auto(
         )
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
-            client = client_class(client_options=options)
+            client = client_class(transport=transport_name, client_options=options)
 
             if use_client_cert_env == "false":
                 expected_client_cert_source = None
@@ -360,7 +342,7 @@ def test_domains_client_mtls_env_auto(
                         expected_client_cert_source = client_cert_source_callback
 
                     patched.return_value = None
-                    client = client_class()
+                    client = client_class(transport=transport_name)
                     patched.assert_called_once_with(
                         credentials=None,
                         credentials_file=None,
@@ -382,7 +364,7 @@ def test_domains_client_mtls_env_auto(
                 return_value=False,
             ):
                 patched.return_value = None
-                client = client_class()
+                client = client_class(transport=transport_name)
                 patched.assert_called_once_with(
                     credentials=None,
                     credentials_file=None,
@@ -409,7 +391,7 @@ def test_domains_client_client_options_scopes(
     options = client_options.ClientOptions(scopes=["1", "2"],)
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -436,7 +418,7 @@ def test_domains_client_client_options_credentials_file(
     options = client_options.ClientOptions(credentials_file="credentials.json")
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file="credentials.json",
@@ -4065,7 +4047,6 @@ def test_domains_base_transport():
         transport.operations_client
 
 
-@requires_google_auth_gte_1_25_0
 def test_domains_base_transport_with_credentials_file():
     # Instantiate the base transport with a credentials file
     with mock.patch.object(
@@ -4086,26 +4067,6 @@ def test_domains_base_transport_with_credentials_file():
         )
 
 
-@requires_google_auth_lt_1_25_0
-def test_domains_base_transport_with_credentials_file_old_google_auth():
-    # Instantiate the base transport with a credentials file
-    with mock.patch.object(
-        google.auth, "load_credentials_from_file", autospec=True
-    ) as load_creds, mock.patch(
-        "google.cloud.domains_v1.services.domains.transports.DomainsTransport._prep_wrapped_messages"
-    ) as Transport:
-        Transport.return_value = None
-        load_creds.return_value = (ga_credentials.AnonymousCredentials(), None)
-        transport = transports.DomainsTransport(
-            credentials_file="credentials.json", quota_project_id="octopus",
-        )
-        load_creds.assert_called_once_with(
-            "credentials.json",
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id="octopus",
-        )
-
-
 def test_domains_base_transport_with_adc():
     # Test the default credentials are used if credentials and credentials_file are None.
     with mock.patch.object(google.auth, "default", autospec=True) as adc, mock.patch(
@@ -4117,7 +4078,6 @@ def test_domains_base_transport_with_adc():
         adc.assert_called_once()
 
 
-@requires_google_auth_gte_1_25_0
 def test_domains_auth_adc():
     # If no credentials are provided, we should use ADC credentials.
     with mock.patch.object(google.auth, "default", autospec=True) as adc:
@@ -4130,23 +4090,10 @@ def test_domains_auth_adc():
         )
 
 
-@requires_google_auth_lt_1_25_0
-def test_domains_auth_adc_old_google_auth():
-    # If no credentials are provided, we should use ADC credentials.
-    with mock.patch.object(google.auth, "default", autospec=True) as adc:
-        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
-        DomainsClient()
-        adc.assert_called_once_with(
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id=None,
-        )
-
-
 @pytest.mark.parametrize(
     "transport_class",
     [transports.DomainsGrpcTransport, transports.DomainsGrpcAsyncIOTransport,],
 )
-@requires_google_auth_gte_1_25_0
 def test_domains_transport_auth_adc(transport_class):
     # If credentials and host are not provided, the transport class should use
     # ADC credentials.
@@ -4160,23 +4107,6 @@ def test_domains_transport_auth_adc(transport_class):
         )
 
 
-@pytest.mark.parametrize(
-    "transport_class",
-    [transports.DomainsGrpcTransport, transports.DomainsGrpcAsyncIOTransport,],
-)
-@requires_google_auth_lt_1_25_0
-def test_domains_transport_auth_adc_old_google_auth(transport_class):
-    # If credentials and host are not provided, the transport class should use
-    # ADC credentials.
-    with mock.patch.object(google.auth, "default", autospec=True) as adc:
-        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
-        transport_class(quota_project_id="octopus")
-        adc.assert_called_once_with(
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id="octopus",
-        )
-
-
 @pytest.mark.parametrize(
     "transport_class,grpc_helpers",
     [
diff --git a/tests/unit/gapic/domains_v1beta1/test_domains.py b/tests/unit/gapic/domains_v1beta1/test_domains.py
index 88d273c..2975393 100644
--- a/tests/unit/gapic/domains_v1beta1/test_domains.py
+++ b/tests/unit/gapic/domains_v1beta1/test_domains.py
@@ -15,7 +15,6 @@
 #
 import os
 import mock
-import packaging.version
 
 import grpc
 from grpc.experimental import aio
@@ -39,9 +38,6 @@
 from google.cloud.domains_v1beta1.services.domains import DomainsClient
 from google.cloud.domains_v1beta1.services.domains import pagers
 from google.cloud.domains_v1beta1.services.domains import transports
-from google.cloud.domains_v1beta1.services.domains.transports.base import (
-    _GOOGLE_AUTH_VERSION,
-)
 from google.cloud.domains_v1beta1.types import domains
 from google.longrunning import operations_pb2
 from google.oauth2 import service_account
@@ -52,20 +48,6 @@
 import google.auth
 
 
-# TODO(busunkim): Once google-auth >= 1.25.0 is required transitively
-# through google-api-core:
-# - Delete the auth "less than" test cases
-# - Delete these pytest markers (Make the "greater than or equal to" tests the default).
-requires_google_auth_lt_1_25_0 = pytest.mark.skipif(
-    packaging.version.parse(_GOOGLE_AUTH_VERSION) >= packaging.version.parse("1.25.0"),
-    reason="This test requires google-auth < 1.25.0",
-)
-requires_google_auth_gte_1_25_0 = pytest.mark.skipif(
-    packaging.version.parse(_GOOGLE_AUTH_VERSION) < packaging.version.parse("1.25.0"),
-    reason="This test requires google-auth >= 1.25.0",
-)
-
-
 def client_cert_source_callback():
     return b"cert bytes", b"key bytes"
 
@@ -200,7 +182,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     options = client_options.ClientOptions(api_endpoint="squid.clam.whelk")
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -217,7 +199,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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()
+            client = client_class(transport=transport_name)
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
@@ -234,7 +216,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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()
+            client = client_class(transport=transport_name)
             patched.assert_called_once_with(
                 credentials=None,
                 credentials_file=None,
@@ -263,7 +245,7 @@ def test_domains_client_client_options(client_class, transport_class, transport_
     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)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -318,7 +300,7 @@ def test_domains_client_mtls_env_auto(
         )
         with mock.patch.object(transport_class, "__init__") as patched:
             patched.return_value = None
-            client = client_class(client_options=options)
+            client = client_class(transport=transport_name, client_options=options)
 
             if use_client_cert_env == "false":
                 expected_client_cert_source = None
@@ -360,7 +342,7 @@ def test_domains_client_mtls_env_auto(
                         expected_client_cert_source = client_cert_source_callback
 
                     patched.return_value = None
-                    client = client_class()
+                    client = client_class(transport=transport_name)
                     patched.assert_called_once_with(
                         credentials=None,
                         credentials_file=None,
@@ -382,7 +364,7 @@ def test_domains_client_mtls_env_auto(
                 return_value=False,
             ):
                 patched.return_value = None
-                client = client_class()
+                client = client_class(transport=transport_name)
                 patched.assert_called_once_with(
                     credentials=None,
                     credentials_file=None,
@@ -409,7 +391,7 @@ def test_domains_client_client_options_scopes(
     options = client_options.ClientOptions(scopes=["1", "2"],)
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file=None,
@@ -436,7 +418,7 @@ def test_domains_client_client_options_credentials_file(
     options = client_options.ClientOptions(credentials_file="credentials.json")
     with mock.patch.object(transport_class, "__init__") as patched:
         patched.return_value = None
-        client = client_class(client_options=options)
+        client = client_class(transport=transport_name, client_options=options)
         patched.assert_called_once_with(
             credentials=None,
             credentials_file="credentials.json",
@@ -4065,7 +4047,6 @@ def test_domains_base_transport():
         transport.operations_client
 
 
-@requires_google_auth_gte_1_25_0
 def test_domains_base_transport_with_credentials_file():
     # Instantiate the base transport with a credentials file
     with mock.patch.object(
@@ -4086,26 +4067,6 @@ def test_domains_base_transport_with_credentials_file():
         )
 
 
-@requires_google_auth_lt_1_25_0
-def test_domains_base_transport_with_credentials_file_old_google_auth():
-    # Instantiate the base transport with a credentials file
-    with mock.patch.object(
-        google.auth, "load_credentials_from_file", autospec=True
-    ) as load_creds, mock.patch(
-        "google.cloud.domains_v1beta1.services.domains.transports.DomainsTransport._prep_wrapped_messages"
-    ) as Transport:
-        Transport.return_value = None
-        load_creds.return_value = (ga_credentials.AnonymousCredentials(), None)
-        transport = transports.DomainsTransport(
-            credentials_file="credentials.json", quota_project_id="octopus",
-        )
-        load_creds.assert_called_once_with(
-            "credentials.json",
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id="octopus",
-        )
-
-
 def test_domains_base_transport_with_adc():
     # Test the default credentials are used if credentials and credentials_file are None.
     with mock.patch.object(google.auth, "default", autospec=True) as adc, mock.patch(
@@ -4117,7 +4078,6 @@ def test_domains_base_transport_with_adc():
         adc.assert_called_once()
 
 
-@requires_google_auth_gte_1_25_0
 def test_domains_auth_adc():
     # If no credentials are provided, we should use ADC credentials.
     with mock.patch.object(google.auth, "default", autospec=True) as adc:
@@ -4130,23 +4090,10 @@ def test_domains_auth_adc():
         )
 
 
-@requires_google_auth_lt_1_25_0
-def test_domains_auth_adc_old_google_auth():
-    # If no credentials are provided, we should use ADC credentials.
-    with mock.patch.object(google.auth, "default", autospec=True) as adc:
-        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
-        DomainsClient()
-        adc.assert_called_once_with(
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id=None,
-        )
-
-
 @pytest.mark.parametrize(
     "transport_class",
     [transports.DomainsGrpcTransport, transports.DomainsGrpcAsyncIOTransport,],
 )
-@requires_google_auth_gte_1_25_0
 def test_domains_transport_auth_adc(transport_class):
     # If credentials and host are not provided, the transport class should use
     # ADC credentials.
@@ -4160,23 +4107,6 @@ def test_domains_transport_auth_adc(transport_class):
         )
 
 
-@pytest.mark.parametrize(
-    "transport_class",
-    [transports.DomainsGrpcTransport, transports.DomainsGrpcAsyncIOTransport,],
-)
-@requires_google_auth_lt_1_25_0
-def test_domains_transport_auth_adc_old_google_auth(transport_class):
-    # If credentials and host are not provided, the transport class should use
-    # ADC credentials.
-    with mock.patch.object(google.auth, "default", autospec=True) as adc:
-        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
-        transport_class(quota_project_id="octopus")
-        adc.assert_called_once_with(
-            scopes=("https://www.googleapis.com/auth/cloud-platform",),
-            quota_project_id="octopus",
-        )
-
-
 @pytest.mark.parametrize(
     "transport_class,grpc_helpers",
     [