diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/async_client.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/async_client.py
index 805a79f28164..905ba90eece4 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/async_client.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/async_client.py
@@ -19,14 +19,17 @@
 from typing import Dict, Sequence, Tuple, Type, Union
 import pkg_resources
 
-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.api_core.client_options import ClientOptions
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
-OptionalRetry = Union[retries.Retry, object]
+try:
+    OptionalRetry = Union[retries.Retry, gapic_v1.method._MethodDefault]
+except AttributeError:  # pragma: NO COVER
+    OptionalRetry = Union[retries.Retry, object]  # type: ignore
 
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/client.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/client.py
index dc6dc79a193b..c54108f6e090 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/client.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/client.py
@@ -14,23 +14,25 @@
 # limitations under the License.
 #
 from collections import OrderedDict
-from distutils import util
 import os
 import re
 from typing import Dict, Optional, Sequence, Tuple, Type, Union
 import pkg_resources
 
-from google.api_core import client_options as client_options_lib  # 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.api_core import client_options as client_options_lib
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport import mtls  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
-OptionalRetry = Union[retries.Retry, object]
+try:
+    OptionalRetry = Union[retries.Retry, gapic_v1.method._MethodDefault]
+except AttributeError:  # pragma: NO COVER
+    OptionalRetry = Union[retries.Retry, object]  # type: ignore
 
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
@@ -318,8 +320,15 @@ def __init__(
             client_options = client_options_lib.ClientOptions()
 
         # Create SSL credentials for mutual TLS if needed.
-        use_client_cert = bool(
-            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
+        if os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") not in (
+            "true",
+            "false",
+        ):
+            raise ValueError(
+                "Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`"
+            )
+        use_client_cert = (
+            os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true"
         )
 
         client_cert_source_func = None
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/base.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/base.py
index d38a289a2571..e03da79fb19e 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/base.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/base.py
@@ -18,11 +18,11 @@
 import pkg_resources
 
 import google.auth  # type: ignore
-import google.api_core  # 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.api_core import operations_v1  # type: ignore
+import google.api_core
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
+from google.api_core import operations_v1
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc.py
index cbf30d5be0ae..b0304cf85813 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc.py
@@ -16,9 +16,9 @@
 import warnings
 from typing import Callable, Dict, Optional, Sequence, Tuple, Union
 
-from google.api_core import grpc_helpers  # type: ignore
-from google.api_core import operations_v1  # type: ignore
-from google.api_core import gapic_v1  # type: ignore
+from google.api_core import grpc_helpers
+from google.api_core import operations_v1
+from google.api_core import gapic_v1
 import google.auth  # type: ignore
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc_asyncio.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc_asyncio.py
index f4b7b5d8f68f..796441945540 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc_asyncio.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1/services/gke_hub/transports/grpc_asyncio.py
@@ -16,9 +16,9 @@
 import warnings
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Tuple, Union
 
-from google.api_core import gapic_v1  # type: ignore
-from google.api_core import grpc_helpers_async  # type: ignore
-from google.api_core import operations_v1  # type: ignore
+from google.api_core import gapic_v1
+from google.api_core import grpc_helpers_async
+from google.api_core import operations_v1
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/async_client.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/async_client.py
index 199905b59a99..24d055f8858c 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/async_client.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/async_client.py
@@ -19,14 +19,17 @@
 from typing import Dict, Sequence, Tuple, Type, Union
 import pkg_resources
 
-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.api_core.client_options import ClientOptions
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
-OptionalRetry = Union[retries.Retry, object]
+try:
+    OptionalRetry = Union[retries.Retry, gapic_v1.method._MethodDefault]
+except AttributeError:  # pragma: NO COVER
+    OptionalRetry = Union[retries.Retry, object]  # type: ignore
 
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/client.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/client.py
index c7dfccb33f19..f7ab895f1175 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/client.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/client.py
@@ -14,23 +14,25 @@
 # limitations under the License.
 #
 from collections import OrderedDict
-from distutils import util
 import os
 import re
 from typing import Dict, Optional, Sequence, Tuple, Type, Union
 import pkg_resources
 
-from google.api_core import client_options as client_options_lib  # 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.api_core import client_options as client_options_lib
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport import mtls  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
 from google.auth.exceptions import MutualTLSChannelError  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
-OptionalRetry = Union[retries.Retry, object]
+try:
+    OptionalRetry = Union[retries.Retry, gapic_v1.method._MethodDefault]
+except AttributeError:  # pragma: NO COVER
+    OptionalRetry = Union[retries.Retry, object]  # type: ignore
 
 from google.api_core import operation  # type: ignore
 from google.api_core import operation_async  # type: ignore
@@ -300,8 +302,15 @@ def __init__(
             client_options = client_options_lib.ClientOptions()
 
         # Create SSL credentials for mutual TLS if needed.
-        use_client_cert = bool(
-            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
+        if os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") not in (
+            "true",
+            "false",
+        ):
+            raise ValueError(
+                "Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`"
+            )
+        use_client_cert = (
+            os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true"
         )
 
         client_cert_source_func = None
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/base.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/base.py
index 75385448fd16..d81686b4d619 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/base.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/base.py
@@ -18,11 +18,11 @@
 import pkg_resources
 
 import google.auth  # type: ignore
-import google.api_core  # 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.api_core import operations_v1  # type: ignore
+import google.api_core
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core import retry as retries
+from google.api_core import operations_v1
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.oauth2 import service_account  # type: ignore
 
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc.py
index ee744c123293..ea3807b0b368 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc.py
@@ -16,9 +16,9 @@
 import warnings
 from typing import Callable, Dict, Optional, Sequence, Tuple, Union
 
-from google.api_core import grpc_helpers  # type: ignore
-from google.api_core import operations_v1  # type: ignore
-from google.api_core import gapic_v1  # type: ignore
+from google.api_core import grpc_helpers
+from google.api_core import operations_v1
+from google.api_core import gapic_v1
 import google.auth  # type: ignore
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore
diff --git a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc_asyncio.py b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc_asyncio.py
index f9d00e7f1391..6f4616513ffd 100644
--- a/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc_asyncio.py
+++ b/packages/google-cloud-gke-hub/google/cloud/gkehub_v1beta1/services/gke_hub_membership_service/transports/grpc_asyncio.py
@@ -16,9 +16,9 @@
 import warnings
 from typing import Awaitable, Callable, Dict, Optional, Sequence, Tuple, Union
 
-from google.api_core import gapic_v1  # type: ignore
-from google.api_core import grpc_helpers_async  # type: ignore
-from google.api_core import operations_v1  # type: ignore
+from google.api_core import gapic_v1
+from google.api_core import grpc_helpers_async
+from google.api_core import operations_v1
 from google.auth import credentials as ga_credentials  # type: ignore
 from google.auth.transport.grpc import SslCredentials  # type: ignore