diff --git a/google-cloud-pubsub/lib/google/cloud/pubsub/service.rb b/google-cloud-pubsub/lib/google/cloud/pubsub/service.rb
index 31bb38f9d128..6fd2bb011c9d 100644
--- a/google-cloud-pubsub/lib/google/cloud/pubsub/service.rb
+++ b/google-cloud-pubsub/lib/google/cloud/pubsub/service.rb
@@ -19,6 +19,7 @@
 require "google/cloud/pubsub/version"
 require "google/cloud/pubsub/v1"
 require "google/gax/errors"
+require "securerandom"
 
 module Google
   module Cloud
@@ -28,6 +29,12 @@ module PubSub
       # methods.
       class Service
         attr_accessor :project, :credentials, :host, :timeout, :client_config
+        ###
+        # The same client_id is used across all streaming pull connections that are created by this client. This is
+        # intentional, as it indicates to the server that any guarantees, such as message ordering, made for a stream
+        # that is disconnected will be made for the stream that is created to replace it. The attr_accessor allows the
+        # value to be replaced for unit testing.
+        attr_accessor :client_id
 
         ##
         # Creates a new Service instance.
@@ -38,6 +45,7 @@ def initialize project, credentials, host: nil, timeout: nil,
           @host = host || V1::PublisherClient::SERVICE_ADDRESS
           @timeout = timeout
           @client_config = client_config || {}
+          @client_id = SecureRandom.uuid.freeze
         end
 
         def channel
diff --git a/google-cloud-pubsub/lib/google/cloud/pubsub/subscriber/stream.rb b/google-cloud-pubsub/lib/google/cloud/pubsub/subscriber/stream.rb
index 721b2efb602e..2daeed8d6cbe 100644
--- a/google-cloud-pubsub/lib/google/cloud/pubsub/subscriber/stream.rb
+++ b/google-cloud-pubsub/lib/google/cloud/pubsub/subscriber/stream.rb
@@ -363,6 +363,7 @@ def initial_input_request
               req.stream_ack_deadline_seconds = @subscriber.deadline
               req.modify_deadline_ack_ids += @inventory.ack_ids
               req.modify_deadline_seconds += @inventory.ack_ids.map { @subscriber.deadline }
+              req.client_id = @subscriber.service.client_id
             end
           end
 
diff --git a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/acknowledge_test.rb b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/acknowledge_test.rb
index fab81860fffb..d475d77fe950 100644
--- a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/acknowledge_test.rb
+++ b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/acknowledge_test.rb
@@ -27,6 +27,7 @@
                           rec_message_hash("rec_message2-msg-goes-here", 1112) }
   let(:rec_msg3_grpc) { Google::Cloud::PubSub::V1::ReceivedMessage.new \
                           rec_message_hash("rec_message3-msg-goes-here", 1113) }
+  let(:client_id) { "my-client-uuid" }
 
   it "can acknowledge a single message" do
     rec_message_msg = "pulled-message"
@@ -38,6 +39,8 @@
     called = false
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |result|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! unless called
@@ -63,6 +66,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
@@ -97,6 +101,8 @@
     called = 0
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! if called.zero?
@@ -119,6 +125,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
diff --git a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/inventory_test.rb b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/inventory_test.rb
index 317ff2ff7dda..89520a741203 100644
--- a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/inventory_test.rb
+++ b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/inventory_test.rb
@@ -27,6 +27,7 @@
                           rec_message_hash("rec_message2-msg-goes-here", 1112) }
   let(:rec_msg3_grpc) { Google::Cloud::PubSub::V1::ReceivedMessage.new \
                           rec_message_hash("rec_message3-msg-goes-here", 1113) }
+  let(:client_id) { "my-client-uuid" }
 
   it "removes a single message from inventory, even when ack or nack are not called" do
     rec_message_msg = "pulled-message"
@@ -38,6 +39,8 @@
     called = false
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |result|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! unless called
@@ -68,6 +71,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
@@ -102,6 +106,8 @@
     called = 0
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! if called.zero?
@@ -128,6 +134,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
diff --git a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/modify_ack_deadline_test.rb b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/modify_ack_deadline_test.rb
index c82a89cd5026..228a8c0065f0 100644
--- a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/modify_ack_deadline_test.rb
+++ b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/modify_ack_deadline_test.rb
@@ -27,6 +27,7 @@
                           rec_message_hash("rec_message2-msg-goes-here", 1112) }
   let(:rec_msg3_grpc) { Google::Cloud::PubSub::V1::ReceivedMessage.new \
                           rec_message_hash("rec_message3-msg-goes-here", 1113) }
+  let(:client_id) { "my-client-uuid" }
 
   it "can modify_ack_deadline a single message" do
     rec_message_msg = "pulled-message"
@@ -38,6 +39,8 @@
     called = false
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! unless called
@@ -63,6 +66,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
@@ -92,6 +96,8 @@
     called = 0
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! if called.zero?
@@ -114,6 +120,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
diff --git a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/nack_test.rb b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/nack_test.rb
index 1eaf2e4e1af1..6887b87e8598 100644
--- a/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/nack_test.rb
+++ b/google-cloud-pubsub/test/google/cloud/pubsub/subscriber/nack_test.rb
@@ -27,6 +27,7 @@
                           rec_message_hash("rec_message2-msg-goes-here", 1112) }
   let(:rec_msg3_grpc) { Google::Cloud::PubSub::V1::ReceivedMessage.new \
                           rec_message_hash("rec_message3-msg-goes-here", 1113) }
+  let(:client_id) { "my-client-uuid" }
 
   it "can nack a single message" do
     rec_message_msg = "pulled-message"
@@ -38,6 +39,8 @@
     called = false
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! unless called
@@ -62,6 +65,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]
@@ -91,6 +95,8 @@
     called = 0
 
     subscription.service.mocked_subscriber = stub
+    subscription.service.client_id = client_id
+
     subscriber = subscription.listen streams: 1 do |msg|
       # flush the initial buffer before any callbacks are processed
       subscriber.buffer.flush! if called.zero?
@@ -113,6 +119,7 @@
 
     _(stub.requests.map(&:to_a)).must_equal [
       [Google::Cloud::PubSub::V1::StreamingPullRequest.new(
+        client_id: client_id,
         subscription: sub_path,
         stream_ack_deadline_seconds: 60
       )]