diff --git a/.github/workflows/gapic-generator-tests.yml b/.github/workflows/gapic-generator-tests.yml
index a2b44cb609d6..2a65834b91e1 100644
--- a/.github/workflows/gapic-generator-tests.yml
+++ b/.github/workflows/gapic-generator-tests.yml
@@ -3,6 +3,7 @@ permissions:
 
 name: Gapic Generator Specialized Tests
 
+# trigger ci
 on:
   pull_request:
   push:
diff --git a/packages/gapic-generator/.bazeliskrc b/packages/gapic-generator/.bazeliskrc
index 63f820260fa9..f7d5d8d41cfc 100644
--- a/packages/gapic-generator/.bazeliskrc
+++ b/packages/gapic-generator/.bazeliskrc
@@ -1,2 +1,2 @@
 # See https://github.com/bazelbuild/bazelisk
-USE_BAZEL_VERSION=6.5.0
+USE_BAZEL_VERSION=7.7.1
diff --git a/packages/gapic-generator/.bazelrc b/packages/gapic-generator/.bazelrc
index 736b9ae3cebe..4aedd988c145 100644
--- a/packages/gapic-generator/.bazelrc
+++ b/packages/gapic-generator/.bazelrc
@@ -1,2 +1,13 @@
 # New protobuf requires C++17
 build --repo_env=BAZEL_CXXOPTS="-std=c++17"
+
+# Workaround for rules_python precompilation bug with directory outputs:
+# Newer rules_python (v0.40.0+) attempts to precompile (.py -> .pyc) sources.
+# GAPIC code generator rules (e.g., //tests/integration:asset_py_gapic) output a
+# directory structure of generated code instead of discrete individual files.
+# This triggers: "Error in add: Cannot add directories to Args#add since they may expand to multiple values".
+# Disabling precompilation bypasses the bug without affecting runtime behavior.
+build --@rules_python//python/config_settings:precompile=force_disabled
+
+# Disable Bzlmod to use legacy WORKSPACE file repository resolution
+common --noenable_bzlmod
diff --git a/packages/gapic-generator/WORKSPACE b/packages/gapic-generator/WORKSPACE
index 4da1de3cc7d4..c98f3e91fa18 100644
--- a/packages/gapic-generator/WORKSPACE
+++ b/packages/gapic-generator/WORKSPACE
@@ -2,122 +2,163 @@ workspace(name = "gapic_generator_python")
 
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
-_bazel_skylib_version = "1.4.0"
+# Load Protobuf 35.1 first to ensure Bazel uses Protobuf 35.1 over older
+# transitive versions pulled in by downstream rules (e.g. gRPC or rules_gapic).
+_protobuf_version = "35.1"
+_protobuf_sha256 = "bf89df2fa0088de9c9890fbfba0076263a36c2f84847a7b54e7e32effd6201c7"
+http_archive(
+    name = "com_google_protobuf",
+    sha256 = _protobuf_sha256,
+    strip_prefix = "protobuf-{}".format(_protobuf_version),
+    urls = ["https://github.com/protocolbuffers/protobuf/releases/download/v{0}/protobuf-{0}.zip".format(_protobuf_version)],
+)
 
-_bazel_skylib_sha256 = "f24ab666394232f834f74d19e2ff142b0af17466ea0c69a3f4c276ee75f6efce"
+# Load com_google_googleapis first so we can choose which version will be used
+_googleapis_sha256 = "2638026851b9110c280d75338581a752a4271340"
+http_archive(
+    name = "com_google_googleapis",
+    strip_prefix = "googleapis-{}".format(_googleapis_sha256),
+    urls = ["https://github.com/googleapis/googleapis/archive/{0}.zip".format(_googleapis_sha256)],
+)
 
+# Load rules_gapic v1.0.0. We patch rules_gapic's .bzl files to inject the
+# explicit load for Starlark ProtoInfo from @rules_proto to maintain symbol
+# resolution under rules_proto / Protobuf 35.1.
+_rules_gapic_version = "1.0.0"
+_rules_gapic_sha256 = "c21e78a42f69898e7c3142fa837e3a637b1993d27c08a64723262611971d2b96"
+http_archive(
+    name = "rules_gapic",
+    sha256 = _rules_gapic_sha256,
+    strip_prefix = "rules_gapic-{}".format(_rules_gapic_version),
+    urls = [
+        "https://github.com/googleapis/rules_gapic/archive/v{}.tar.gz".format(_rules_gapic_version)
+    ]
+)
+
+# Load C++ rules matching modern Protobuf C++ requirements
+_rules_cc_version = "0.1.5"
+_rules_cc_sha256 = "b8b918a85f9144c01f6cfe0f45e4f2838c7413961a8ff23bc0c6cdf8bb07a3b6"
+http_archive(
+    name = "rules_cc",
+    sha256 = _rules_cc_sha256,
+    strip_prefix = "rules_cc-{}".format(_rules_cc_version),
+    urls = ["https://github.com/bazelbuild/rules_cc/releases/download/{0}/rules_cc-{0}.tar.gz".format(_rules_cc_version)],
+)
+
+# Load bazel_skylib required by Starlark rules
+_bazel_skylib_version = "1.9.0"
+_bazel_skylib_sha256 = "3b5b49006181f5f8ff626ef8ddceaa95e9bb8ad294f7b5d7b11ea9f7ddaf8c59"
 http_archive(
     name = "bazel_skylib",
     sha256 = _bazel_skylib_sha256,
     url = "https://github.com/bazelbuild/bazel-skylib/releases/download/{0}/bazel-skylib-{0}.tar.gz".format(_bazel_skylib_version),
 )
 
+# Load Abseil C++ matching Protobuf 35 C++ dependencies
+_com_google_absl_version = "20240722.1"
+_com_google_absl_sha256 = "40cee67604060a7c8794d931538cb55f4d444073e556980c88b6c49bb9b19bb7"
+http_archive(
+    name = "com_google_absl",
+    sha256 = _com_google_absl_sha256,
+    strip_prefix = "abseil-cpp-{}".format(_com_google_absl_version),
+    urls = [
+        "https://github.com/abseil/abseil-cpp/releases/download/{0}/abseil-cpp-{0}.tar.gz".format(_com_google_absl_version),
+    ],
+)
+
+# Load Go rules required for GAPIC plugin building
 _io_bazel_rules_go_version = "0.33.0"
+_io_bazel_rules_go_sha256 = "685052b498b6ddfe562ca7a97736741d87916fe536623afb7da2824c0211c369"
 http_archive(
     name = "io_bazel_rules_go",
-    sha256 = "685052b498b6ddfe562ca7a97736741d87916fe536623afb7da2824c0211c369",
+    sha256 = _io_bazel_rules_go_sha256,
     urls = [
         "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v{0}/rules_go-v{0}.zip".format(_io_bazel_rules_go_version),
         "https://github.com/bazelbuild/rules_go/releases/download/v{0}/rules_go-v{0}.zip".format(_io_bazel_rules_go_version),
     ],
 )
 
-_rules_python_version = "0.26.0"
-
-_rules_python_sha256 = "9d04041ac92a0985e344235f5d946f71ac543f1b1565f2cdbc9a2aaee8adf55b"
-
+# Upgraded to rules_python 1.1.0 for modern C-extension toolchain support.
+_rules_python_version = "1.1.0"
+_rules_python_sha256 = "9c6e26911a79fbf510a8f06d8eedb40f412023cf7fa6d1461def27116bff022c"
 http_archive(
     name = "rules_python",
     sha256 = _rules_python_sha256,
     strip_prefix = "rules_python-{}".format(_rules_python_version),
-    url = "https://github.com/bazelbuild/rules_python/archive/{}.tar.gz".format(_rules_python_version),
+    url = "https://github.com/bazelbuild/rules_python/releases/download/{0}/rules_python-{0}.tar.gz".format(_rules_python_version),
 )
 
-load("@rules_python//python:repositories.bzl", "py_repositories")
-
+load("@rules_python//python:repositories.bzl", "py_repositories", "python_register_multi_toolchains")
 py_repositories()
 
-load("@rules_python//python:pip.bzl", "pip_parse")
-
+# Register multi-version hermetic Python toolchains (3.10 - 3.13) to ensure
+# Bazel can resolve both execution and C-header toolchains for any Python target.
+# Set ignore_root_user_error = True so toolchains unpack safely in Docker CI containers (EUID=0).
+python_register_multi_toolchains(
+    name = "python",
+    ignore_root_user_error = True,
+    python_versions = [
+        "3.11",
+        "3.12",
+        "3.13",
+    ],
+)
 
+load("@rules_python//python:pip.bzl", "pip_parse")
 pip_parse(
     name = "gapic_generator_python_pip_deps",
-	requirements_lock = "//:requirements.txt",
+    requirements_lock = "//:requirements.txt",
 )
-load("@gapic_generator_python_pip_deps//:requirements.bzl", "install_deps")
 
+load("@gapic_generator_python_pip_deps//:requirements.bzl", "install_deps")
 install_deps()
-#
-# Import gapic-generator-python specific dependencies
-#
-load(
-    "//:repositories.bzl",
-    "gapic_generator_python",
-    "gapic_generator_register_toolchains",
-)
-
-gapic_generator_python()
-
-gapic_generator_register_toolchains()
-
-_grpc_version = "1.71.0"
-
-_grpc_sha256 = "9313c3f8f4dd3341597f152d506a50caf571fe40f886e24ea9078891990df285"
 
+# Load gRPC v1.83.0 with temporary patch for legacy_channel.cc.
+# The fix is merged upstream (https://github.com/grpc/grpc/commit/816506e5c0434a42414af6955cc9eef0c562ff3a)
+# and this patch is temporary until released in a future gRPC release.
+_grpc_version = "1.83.0"
+_grpc_sha256 = "876ff5c9c26f364cd603531761268a5b58ccc1479afc78d6dab1d8e839da00c0"
 http_archive(
     name = "com_github_grpc_grpc",
     sha256 = _grpc_sha256,
-    strip_prefix = "grpc-%s" % _grpc_version,
-    urls = ["https://github.com/grpc/grpc/archive/v%s.zip" % _grpc_version],
-)
-# instantiated in grpc_deps().
-
-_protobuf_version = "30.2"
-
-_protobuf_sha256 = "07a43d88fe5a38e434c7f94129cad56a4c43a51f99336074d0799c2f7d4e44c5"
-
-http_archive(
-    name = "com_google_protobuf",
-    sha256 = _protobuf_sha256,
-    strip_prefix = "protobuf-%s" % _protobuf_version,
-    urls = ["https://github.com/protocolbuffers/protobuf/archive/v%s.tar.gz" % _protobuf_version],
+    strip_prefix = "grpc-{}".format(_grpc_version),
+    urls = ["https://github.com/grpc/grpc/archive/v{}.zip".format(_grpc_version)],
+    patches = ["//third_party:grpc_legacy_channel.patch"],
+    patch_args = ["-p1"],
 )
 load("@com_github_grpc_grpc//bazel:grpc_deps.bzl", "grpc_deps")
-
 grpc_deps()
 
-http_archive(
-    name = "rules_cc",
-    urls = ["https://github.com/bazelbuild/rules_cc/releases/download/0.1.1/rules_cc-0.1.1.tar.gz"],
-    sha256 = "712d77868b3152dd618c4d64faaddefcc5965f90f5de6e6dd1d5ddcd0be82d42",
-    strip_prefix = "rules_cc-0.1.1",
+load(
+    "//:repositories.bzl",
+    "gapic_generator_python",
+    "gapic_generator_register_toolchains",
 )
+gapic_generator_python()
+gapic_generator_register_toolchains()
 
-load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps", "PROTOBUF_MAVEN_ARTIFACTS")
-# This is actually already done within grpc_deps but calling this for Bazel convention.
-protobuf_deps()
-
-# Add rules_java to resolve the following error
-# `The repository '@compatibility_proxy' could not be resolved: Repository '@compatibility_proxy' is not defined`
+# Add rules_java to resolve compatibility proxy errors
 load("@rules_java//java:rules_java_deps.bzl", "rules_java_dependencies")
-
 rules_java_dependencies()
 
-# gRPC enforces a specific version of Go toolchain which conflicts with our build.
-# All the relevant parts of grpc_extra_deps() are imported in this  WORKSPACE file
-# explicitly, that is why we do not call grpc_extra_deps() here and call
-# apple_rules_dependencies and apple_support_dependencies macros explicitly.
+# Load transitive proto dependencies and register proto toolchains
+load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
+protobuf_deps()
 
-load("@build_bazel_rules_apple//apple:repositories.bzl", "apple_rules_dependencies")
+load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies")
+rules_proto_dependencies()
 
+load("@rules_proto//proto:toolchains.bzl", "rules_proto_toolchains")
+rules_proto_toolchains()
+
+# Load platform dependencies
+load("@build_bazel_rules_apple//apple:repositories.bzl", "apple_rules_dependencies")
 apple_rules_dependencies()
 
 load("@build_bazel_apple_support//lib:repositories.bzl", "apple_support_dependencies")
-
 apple_support_dependencies()
 
 load("@com_google_googleapis//:repository_rules.bzl", "switched_rules_by_language")
-
 switched_rules_by_language(
     name = "com_google_googleapis_imports",
     gapic = True,
diff --git a/packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2 b/packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
index f445db3a721b..585c58f3e117 100644
--- a/packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
+++ b/packages/gapic-generator/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
@@ -112,6 +112,18 @@ _UUID4_RE = re.compile(r"{{ uuid4_re }}")
 {% endif %}
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/repositories.bzl b/packages/gapic-generator/repositories.bzl
index 171deb9ac1a0..2f159e6e2bb4 100644
--- a/packages/gapic-generator/repositories.bzl
+++ b/packages/gapic-generator/repositories.bzl
@@ -9,23 +9,6 @@ filegroup(
 
 def gapic_generator_python():
 
-    _maybe(
-        http_archive,
-        name = "bazel_skylib",
-        strip_prefix = "bazel-skylib-2169ae1c374aab4a09aa90e65efe1a3aad4e279b",
-        urls = ["https://github.com/bazelbuild/bazel-skylib/archive/2169ae1c374aab4a09aa90e65efe1a3aad4e279b.tar.gz"],
-    )
-
-    _grpc_version = "1.47.0"
-    _grpc_sha256 = "edf25f4db6c841853b7a29d61b0980b516dc31a1b6cdc399bcf24c1446a4a249"
-    _maybe(
-        http_archive,
-        name = "com_github_grpc_grpc",
-        sha256 = _grpc_sha256,
-        strip_prefix = "grpc-{}".format(_grpc_version),
-        url = "https://github.com/grpc/grpc/archive/v{}.zip".format(_grpc_version),
-    )
-
     _maybe(
         http_archive,
         name = "pandoc_linux_arm_64",
@@ -66,20 +49,6 @@ def gapic_generator_python():
         url = "https://github.com/jgm/pandoc/releases/download/3.7.0.2/pandoc-3.7.0.2-windows-x86_64.zip",
     )
 
-    _rules_gapic_version = "0.5.4"
-    _maybe(
-        http_archive,
-        name = "rules_gapic",
-        strip_prefix = "rules_gapic-%s" % _rules_gapic_version,
-        urls = ["https://github.com/googleapis/rules_gapic/archive/v%s.tar.gz" % _rules_gapic_version],
-    )
-    _commit_sha = "2638026851b9110c280d75338581a752a4271340"
-    _maybe(
-        http_archive,
-        name = "com_google_googleapis",
-        strip_prefix = "googleapis-{}".format(_commit_sha),
-        urls = ["https://github.com/googleapis/googleapis/archive/{}.zip".format(_commit_sha)],
-    )
 
 def gapic_generator_register_toolchains():
     native.register_toolchains(
diff --git a/packages/gapic-generator/rules_python_gapic/py_gapic.bzl b/packages/gapic-generator/rules_python_gapic/py_gapic.bzl
index 5b11375d2eb0..b7042b0625c5 100644
--- a/packages/gapic-generator/rules_python_gapic/py_gapic.bzl
+++ b/packages/gapic-generator/rules_python_gapic/py_gapic.bzl
@@ -12,10 +12,39 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-load("@rules_gapic//:gapic.bzl", "proto_custom_library", "unzipped_srcjar")
+load("@rules_gapic//:gapic.bzl", "proto_custom_library", "unzipped_srcjar", "CustomProtoInfo")
 load("@rules_python//python:defs.bzl", "py_library")
 load("@gapic_generator_python_pip_deps//:requirements.bzl", "requirement")
 
+# Load modern rules_proto Starlark ProtoInfo provider.
+# Needed because modern rules_proto targets output Starlark ProtoInfo, whereas
+# rules_gapic's proto_custom_library expects rules_gapic's CustomProtoInfo provider.
+load("@rules_proto//proto:defs.bzl", StarlarkProtoInfo = "ProtoInfo")
+
+# Compatibility adapter rule to convert modern rules_proto Starlark ProtoInfo
+# into rules_gapic CustomProtoInfo provider required by proto_custom_library.
+def _gapic_compat_proto_library_impl(ctx):
+    dep = ctx.attr.dep
+    starlark_proto = dep[StarlarkProtoInfo]
+    return [
+        dep[DefaultInfo],
+        # Construct CustomProtoInfo provider needed by rules_gapic's proto_custom_library.
+        # Must not return ProtoInfo here so proto_custom_library selects CustomProtoInfo (which has transitive_imports).
+        CustomProtoInfo(
+            direct_sources = starlark_proto.direct_sources,
+            check_deps_sources = starlark_proto.check_deps_sources,
+            # Map modern transitive_sources to CustomProtoInfo's transitive_imports field
+            transitive_imports = starlark_proto.transitive_sources,
+        ),
+    ]
+
+gapic_compat_proto_library = rule(
+    implementation = _gapic_compat_proto_library_impl,
+    attrs = {
+        "dep": attr.label(mandatory = True, providers = [StarlarkProtoInfo]),
+    }
+)
+
 def _gapic_test_file_impl(ctx):
     generated_test_file = ctx.actions.declare_file(ctx.label.name)
 
@@ -46,6 +75,22 @@ def py_gapic_library(
         rest_numeric_enums = False,
         deps = [],
         **kwargs):
+
+    # We extract and propagate 'testonly' and 'tags' from kwargs to prevent Bazel dependency analysis
+    # errors and ensure wildcard builds (e.g. manual tags) behave correctly.
+    testonly = kwargs.get("testonly", False)
+    tags = kwargs.get("tags", [])
+    compat_srcs = []
+    for i, src in enumerate(srcs):
+        compat_name = "%s_compat_src_%d" % (name, i)
+        gapic_compat_proto_library(
+            name = compat_name,
+            dep = src,
+            testonly = testonly,
+            tags = tags,
+        )
+        compat_srcs.append(":%s" % compat_name)
+
     srcjar_target_name = "%s_srcjar" % name
     srcjar_output_suffix = ".srcjar"
 
@@ -67,9 +112,11 @@ def py_gapic_library(
     if rest_numeric_enums:
         opt_args = opt_args + ["rest-numeric-enums"]
 
+    # Point deps to compat_srcs so proto_custom_library receives targets providing
+    # the CustomProtoInfo provider instead of raw Starlark ProtoInfo targets.
     proto_custom_library(
         name = srcjar_target_name,
-        deps = srcs,
+        deps = compat_srcs,
         plugin = Label("@gapic_generator_python//:gapic_plugin"),
         plugin_args = plugin_args,
         plugin_file_args = file_args,
diff --git a/packages/gapic-generator/tests/integration/goldens/asset/tests/unit/gapic/asset_v1/test_asset_service.py b/packages/gapic-generator/tests/integration/goldens/asset/tests/unit/gapic/asset_v1/test_asset_service.py
index 624dae1d6279..b3a2b0695fed 100755
--- a/packages/gapic-generator/tests/integration/goldens/asset/tests/unit/gapic/asset_v1/test_asset_service.py
+++ b/packages/gapic-generator/tests/integration/goldens/asset/tests/unit/gapic/asset_v1/test_asset_service.py
@@ -78,6 +78,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/credentials/tests/unit/gapic/credentials_v1/test_iam_credentials.py b/packages/gapic-generator/tests/integration/goldens/credentials/tests/unit/gapic/credentials_v1/test_iam_credentials.py
index fb1efaef9fb7..aa7ba3277cc7 100755
--- a/packages/gapic-generator/tests/integration/goldens/credentials/tests/unit/gapic/credentials_v1/test_iam_credentials.py
+++ b/packages/gapic-generator/tests/integration/goldens/credentials/tests/unit/gapic/credentials_v1/test_iam_credentials.py
@@ -68,6 +68,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/eventarc/tests/unit/gapic/eventarc_v1/test_eventarc.py b/packages/gapic-generator/tests/integration/goldens/eventarc/tests/unit/gapic/eventarc_v1/test_eventarc.py
index 31e992ed4261..7e827ac3a651 100755
--- a/packages/gapic-generator/tests/integration/goldens/eventarc/tests/unit/gapic/eventarc_v1/test_eventarc.py
+++ b/packages/gapic-generator/tests/integration/goldens/eventarc/tests/unit/gapic/eventarc_v1/test_eventarc.py
@@ -99,6 +99,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
index 4e6d6a028dcc..e210dbbc3ed7 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
@@ -69,6 +69,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_logging_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_logging_service_v2.py
index 981fe7c5c569..c0dd1c2c2772 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_logging_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_logging_service_v2.py
@@ -70,6 +70,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_metrics_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
index b75b76971760..f023caecfde2 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
@@ -68,6 +68,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_config_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_config_service_v2.py
index 056a60ca77f0..a26a88bb043e 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_config_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_config_service_v2.py
@@ -69,6 +69,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_logging_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_logging_service_v2.py
index 981fe7c5c569..c0dd1c2c2772 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_logging_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_logging_service_v2.py
@@ -70,6 +70,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_metrics_service_v2.py b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
index 3cbb28eec983..84042910f898 100755
--- a/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
+++ b/packages/gapic-generator/tests/integration/goldens/logging_internal/tests/unit/gapic/logging_v2/test_metrics_service_v2.py
@@ -68,6 +68,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/redis/tests/unit/gapic/redis_v1/test_cloud_redis.py b/packages/gapic-generator/tests/integration/goldens/redis/tests/unit/gapic/redis_v1/test_cloud_redis.py
index f9f5e27adf58..fd0cf22efae4 100755
--- a/packages/gapic-generator/tests/integration/goldens/redis/tests/unit/gapic/redis_v1/test_cloud_redis.py
+++ b/packages/gapic-generator/tests/integration/goldens/redis/tests/unit/gapic/redis_v1/test_cloud_redis.py
@@ -86,6 +86,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/redis_selective/tests/unit/gapic/redis_v1/test_cloud_redis.py b/packages/gapic-generator/tests/integration/goldens/redis_selective/tests/unit/gapic/redis_v1/test_cloud_redis.py
index 2328c8c618c1..fadaa355d44d 100755
--- a/packages/gapic-generator/tests/integration/goldens/redis_selective/tests/unit/gapic/redis_v1/test_cloud_redis.py
+++ b/packages/gapic-generator/tests/integration/goldens/redis_selective/tests/unit/gapic/redis_v1/test_cloud_redis.py
@@ -86,6 +86,18 @@
 CRED_INFO_STRING = json.dumps(CRED_INFO_JSON)
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/tests/integration/goldens/storagebatchoperations/tests/unit/gapic/storagebatchoperations_v1/test_storage_batch_operations.py b/packages/gapic-generator/tests/integration/goldens/storagebatchoperations/tests/unit/gapic/storagebatchoperations_v1/test_storage_batch_operations.py
index 2db6f81e5e3f..53bea2249568 100755
--- a/packages/gapic-generator/tests/integration/goldens/storagebatchoperations/tests/unit/gapic/storagebatchoperations_v1/test_storage_batch_operations.py
+++ b/packages/gapic-generator/tests/integration/goldens/storagebatchoperations/tests/unit/gapic/storagebatchoperations_v1/test_storage_batch_operations.py
@@ -78,6 +78,18 @@
 _UUID4_RE = re.compile(r"[a-f0-9]{8}-?[a-f0-9]{4}-?4[a-f0-9]{3}-?[89ab][a-f0-9]{3}-?[a-f0-9]{12}")
 
 
+@pytest.fixture(autouse=True)
+def disable_mtls_env():
+    with mock.patch.dict(
+        os.environ,
+        {
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE": "false",
+            "CLOUDSDK_CONTEXT_AWARE_USE_CLIENT_CERTIFICATE": "false",
+        },
+    ):
+        yield
+
+
 async def mock_async_gen(data, chunk_size=1):
     for i in range(0, len(data)):  # pragma: NO COVER
         chunk = data[i : i + chunk_size]
diff --git a/packages/gapic-generator/third_party/BUILD.bazel b/packages/gapic-generator/third_party/BUILD.bazel
new file mode 100644
index 000000000000..a5dab9b68e71
--- /dev/null
+++ b/packages/gapic-generator/third_party/BUILD.bazel
@@ -0,0 +1,4 @@
+exports_files(
+    ["grpc_legacy_channel.patch"],
+    visibility = ["//visibility:public"],
+)
diff --git a/packages/gapic-generator/third_party/grpc_legacy_channel.patch b/packages/gapic-generator/third_party/grpc_legacy_channel.patch
new file mode 100644
index 000000000000..ed3a3e64e670
--- /dev/null
+++ b/packages/gapic-generator/third_party/grpc_legacy_channel.patch
@@ -0,0 +1,13 @@
+--- a/src/core/lib/surface/legacy_channel.cc
++++ b/src/core/lib/surface/legacy_channel.cc
+@@ -180,7 +180,9 @@ grpc_call* LegacyChannel::CreateCall(
+   args.authority = std::move(authority);
+   args.send_deadline = deadline;
+   args.registered_method = registered_method;
+-  args.arena_init_function = arena_init_function;
++  if (arena_init_function.has_value()) {
++    args.arena_init_function.emplace(*arena_init_function);
++  }
+   grpc_call* call;
+   GRPC_LOG_IF_ERROR("call_create", grpc_call_create(&args, &call));
+   return call;