diff --git a/CHANGELOG.md b/CHANGELOG.md
index b9252ae9..8aa0c5f8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,18 @@
 
 [1]: https://pypi.org/project/google-cloud-tasks/#history
 
+## [2.9.1](https://github.com/googleapis/python-tasks/compare/v2.9.0...v2.9.1) (2022-06-06)
+
+
+### Bug Fixes
+
+* **deps:** require protobuf <4.0.0dev ([#262](https://github.com/googleapis/python-tasks/issues/262)) ([db23558](https://github.com/googleapis/python-tasks/commit/db23558d053d56ff84a4447f7af2525ff4459309))
+
+
+### Documentation
+
+* fix changelog header to consistent size ([#263](https://github.com/googleapis/python-tasks/issues/263)) ([048d907](https://github.com/googleapis/python-tasks/commit/048d907b1929f2ced1dc1d1b3536f38265994330))
+
 ## [2.9.0](https://github.com/googleapis/python-tasks/compare/v2.8.1...v2.9.0) (2022-05-05)
 
 
@@ -21,7 +33,7 @@
 
 * fix type in docstring for map fields ([7b7a294](https://github.com/googleapis/python-tasks/commit/7b7a2946a8554a06d8fdc57b13c2726c5d8a443b))
 
-### [2.8.1](https://github.com/googleapis/python-tasks/compare/v2.8.0...v2.8.1) (2022-03-05)
+## [2.8.1](https://github.com/googleapis/python-tasks/compare/v2.8.0...v2.8.1) (2022-03-05)
 
 
 ### Bug Fixes
@@ -41,14 +53,14 @@
 
 * resolve DuplicateCredentialArgs error when using credentials_file ([8dd8aec](https://github.com/googleapis/python-tasks/commit/8dd8aec79d2302007e3f9511daeab817f05d2aa6))
 
-### [2.7.2](https://www.github.com/googleapis/python-tasks/compare/v2.7.1...v2.7.2) (2022-01-08)
+## [2.7.2](https://www.github.com/googleapis/python-tasks/compare/v2.7.1...v2.7.2) (2022-01-08)
 
 
 ### Documentation
 
 * fix docstring formatting ([#196](https://www.github.com/googleapis/python-tasks/issues/196)) ([e7a3461](https://www.github.com/googleapis/python-tasks/commit/e7a3461a34229c210e63590370fa6eee4d06630a))
 
-### [2.7.1](https://www.github.com/googleapis/python-tasks/compare/v2.7.0...v2.7.1) (2021-11-01)
+## [2.7.1](https://www.github.com/googleapis/python-tasks/compare/v2.7.0...v2.7.1) (2021-11-01)
 
 
 ### Bug Fixes
@@ -82,21 +94,21 @@
 
 * add context manager support in client ([#173](https://www.github.com/googleapis/python-tasks/issues/173)) ([ceec8f1](https://www.github.com/googleapis/python-tasks/commit/ceec8f173af696d26cf367af2d969bf98987df2a))
 
-### [2.5.3](https://www.github.com/googleapis/python-tasks/compare/v2.5.2...v2.5.3) (2021-09-30)
+## [2.5.3](https://www.github.com/googleapis/python-tasks/compare/v2.5.2...v2.5.3) (2021-09-30)
 
 
 ### Bug Fixes
 
 * improper types in pagers generation ([0feec1e](https://www.github.com/googleapis/python-tasks/commit/0feec1e0d1e4847e2722920c8afdc597ecd92e3f))
 
-### [2.5.2](https://www.github.com/googleapis/python-tasks/compare/v2.5.1...v2.5.2) (2021-09-24)
+## [2.5.2](https://www.github.com/googleapis/python-tasks/compare/v2.5.1...v2.5.2) (2021-09-24)
 
 
 ### Bug Fixes
 
 * add 'dict' annotation type to 'request' ([42d768b](https://www.github.com/googleapis/python-tasks/commit/42d768b9f302aef3258f4abc413199070bcd2a8d))
 
-### [2.5.1](https://www.github.com/googleapis/python-tasks/compare/v2.5.0...v2.5.1) (2021-07-28)
+## [2.5.1](https://www.github.com/googleapis/python-tasks/compare/v2.5.0...v2.5.1) (2021-07-28)
 
 
 ### Bug Fixes
diff --git a/samples/snippets/requirements.txt b/samples/snippets/requirements.txt
index f2b4ae7f..55dd827e 100644
--- a/samples/snippets/requirements.txt
+++ b/samples/snippets/requirements.txt
@@ -1 +1 @@
-google-cloud-tasks==2.8.1
+google-cloud-tasks==2.9.0
diff --git a/setup.py b/setup.py
index a447bd0f..910b6b10 100644
--- a/setup.py
+++ b/setup.py
@@ -21,7 +21,7 @@
 
 name = "google-cloud-tasks"
 description = "Cloud Tasks API API client library"
-version = "2.9.0"
+version = "2.9.1"
 release_status = "Development Status :: 5 - Production/Stable"
 dependencies = [
     # NOTE: Maintainers, please do not require google-api-core>=2.x.x
@@ -29,7 +29,8 @@
     # https://github.com/googleapis/google-cloud-python/issues/10566
     "google-api-core[grpc] >= 1.31.5, <3.0.0dev,!=2.0.*,!=2.1.*,!=2.2.*,!=2.3.0",
     "grpc-google-iam-v1 >= 0.12.4, <1.0.0dev",
-    "proto-plus >= 1.15.0",
+    "proto-plus >= 1.15.0, <2.0.0dev",
+    "protobuf >= 3.19.0, <4.0.0dev",
 ]
 
 extras = {"libcst": "libcst >= 0.2.5"}
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 654ad19f..c4e0fd7d 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -9,3 +9,4 @@ google-api-core==1.31.5
 grpc-google-iam-v1==0.12.4
 proto-plus==1.15.0
 libcst==0.2.5
+protobuf==3.19.0
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
index e69de29b..c4e0fd7d 100644
--- a/testing/constraints-3.7.txt
+++ b/testing/constraints-3.7.txt
@@ -0,0 +1,12 @@
+# This constraints file is used to check that lower bounds
+# are correct in setup.py
+# List *all* library dependencies and extras in this file.
+# Pin the version to the lower bound.
+#
+# 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==1.31.5
+grpc-google-iam-v1==0.12.4
+proto-plus==1.15.0
+libcst==0.2.5
+protobuf==3.19.0
diff --git a/tests/unit/gapic/tasks_v2/test_cloud_tasks.py b/tests/unit/gapic/tasks_v2/test_cloud_tasks.py
index 35dda73e..ed472878 100644
--- a/tests/unit/gapic/tasks_v2/test_cloud_tasks.py
+++ b/tests/unit/gapic/tasks_v2/test_cloud_tasks.py
@@ -13,9 +13,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-import math
 import os
 
+# try/except added for compatibility with python < 3.8
+try:
+    from unittest import mock
+    from unittest.mock import AsyncMock
+except ImportError:
+    import mock
+
+import math
+
 from google.api_core import gapic_v1, grpc_helpers, grpc_helpers_async, path_template
 from google.api_core import client_options
 from google.api_core import exceptions as core_exceptions
@@ -34,7 +42,6 @@
 from google.type import expr_pb2  # type: ignore
 import grpc
 from grpc.experimental import aio
-import mock
 from proto.marshal.rules.dates import DurationRule, TimestampRule
 import pytest
 
diff --git a/tests/unit/gapic/tasks_v2beta2/test_cloud_tasks.py b/tests/unit/gapic/tasks_v2beta2/test_cloud_tasks.py
index ea08fcef..87715122 100644
--- a/tests/unit/gapic/tasks_v2beta2/test_cloud_tasks.py
+++ b/tests/unit/gapic/tasks_v2beta2/test_cloud_tasks.py
@@ -13,9 +13,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-import math
 import os
 
+# try/except added for compatibility with python < 3.8
+try:
+    from unittest import mock
+    from unittest.mock import AsyncMock
+except ImportError:
+    import mock
+
+import math
+
 from google.api_core import gapic_v1, grpc_helpers, grpc_helpers_async, path_template
 from google.api_core import client_options
 from google.api_core import exceptions as core_exceptions
@@ -34,7 +42,6 @@
 from google.type import expr_pb2  # type: ignore
 import grpc
 from grpc.experimental import aio
-import mock
 from proto.marshal.rules.dates import DurationRule, TimestampRule
 import pytest
 
diff --git a/tests/unit/gapic/tasks_v2beta3/test_cloud_tasks.py b/tests/unit/gapic/tasks_v2beta3/test_cloud_tasks.py
index 86fa27e3..f47f6940 100644
--- a/tests/unit/gapic/tasks_v2beta3/test_cloud_tasks.py
+++ b/tests/unit/gapic/tasks_v2beta3/test_cloud_tasks.py
@@ -13,9 +13,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-import math
 import os
 
+# try/except added for compatibility with python < 3.8
+try:
+    from unittest import mock
+    from unittest.mock import AsyncMock
+except ImportError:
+    import mock
+
+import math
+
 from google.api_core import gapic_v1, grpc_helpers, grpc_helpers_async, path_template
 from google.api_core import client_options
 from google.api_core import exceptions as core_exceptions
@@ -34,7 +42,6 @@
 from google.type import expr_pb2  # type: ignore
 import grpc
 from grpc.experimental import aio
-import mock
 from proto.marshal.rules.dates import DurationRule, TimestampRule
 import pytest