@@ -13,6 +13,7 @@
 # limitations under the License.
 
 load(":spanner_client_integration_tests.bzl", "spanner_client_integration_tests")
+load(":spanner_client_session_mode_sensitive_integration_tests.bzl", "spanner_client_session_mode_sensitive_integration_tests")
 
 package(default_visibility = ["//visibility:private"])
 
@@ -37,3 +38,30 @@ licenses(["notice"])  # Apache 2.0
         "@com_google_googletest//:gtest_main",
     ],
 ) for test in spanner_client_integration_tests]
+
+VARIATIONS = {
+    "session-pool": {"GOOGLE_CLOUD_CPP_SPANNER_TESTING_SESSION_MODE": "pool"},
+    "session-multiplexed": {"GOOGLE_CLOUD_CPP_SPANNER_TESTING_SESSION_MODE": "multiplexed"},
+}
+
+[cc_test(
+    name = test.replace("/", "_").replace(".cc", "") + "-" + v_label,
+    timeout = "eternal",
+    srcs = [test],
+    env = v_env,
+    tags = [
+        "integration-test",
+        "integration-test-" + v_label,
+    ],
+    deps = [
+        "//:common",
+        "//:spanner",
+        "//:spanner_mocks",
+        "//google/cloud/spanner:spanner_client_testing_private",
+        "//google/cloud/testing_util:google_cloud_cpp_testing_grpc_private",
+        "//google/cloud/testing_util:google_cloud_cpp_testing_private",
+        "//protos:system_includes",
+        "//protos/google/cloud/spanner/testing:singer_cc_proto",
+        "@com_google_googletest//:gtest_main",
+    ],
+) for test in spanner_client_session_mode_sensitive_integration_tests for v_label, v_env in VARIATIONS.items()]
@@ -25,23 +25,31 @@ function (spanner_client_define_integration_tests)
         # cmake-format: sort
         backup_extra_integration_test.cc
         backup_integration_test.cc
-        client_integration_test.cc
         client_stress_test.cc
         data_types_integration_test.cc
         database_admin_integration_test.cc
         instance_admin_integration_test.cc
         session_pool_integration_test.cc)
 
+    set(spanner_client_session_mode_sensitive_integration_tests
+        # cmake-format: sort
+        client_integration_test.cc)
+
     # Export the list of unit tests to a .bzl file so we do not need to maintain
     # the list in two places.
     export_list_to_bazel("spanner_client_integration_tests.bzl"
                          "spanner_client_integration_tests" YEAR "2019")
+    export_list_to_bazel(
+        "spanner_client_session_mode_sensitive_integration_tests.bzl"
+        "spanner_client_session_mode_sensitive_integration_tests" YEAR "2025")
 
     # Create a custom target so we can say "build all the tests"
     add_custom_target(spanner-client-integration-tests)
 
     # Generate a target for each unit test.
-    foreach (fname ${spanner_client_integration_tests})
+    foreach (fname IN
+             LISTS ${spanner_client_integration_tests}
+                   ${spanner_client_session_mode_sensitive_integration_tests})
         google_cloud_cpp_add_executable(target "spanner" "${fname}")
         target_link_libraries(
             ${target}
 
@@ -18,6 +18,7 @@
 #include "google/cloud/spanner/mutations.h"
 #include "google/cloud/spanner/testing/database_integration_test.h"
 #include "google/cloud/credentials.h"
+#include "google/cloud/internal/getenv.h"
 #include "google/cloud/internal/random.h"
 #include "google/cloud/testing_util/status_matchers.h"
 #include <gmock/gmock.h>
@@ -49,9 +50,15 @@ class ClientIntegrationTest : public spanner_testing::DatabaseIntegrationTest {
  protected:
   static void SetUpTestSuite() {
     spanner_testing::DatabaseIntegrationTest::SetUpTestSuite();
-    client_ = std::make_unique<Client>(MakeConnection(
-        GetDatabase(),
-        Options{}.set<GrpcCompressionAlgorithmOption>(GRPC_COMPRESS_GZIP)));
+    auto options =
+        Options{}.set<GrpcCompressionAlgorithmOption>(GRPC_COMPRESS_GZIP);
+    auto session_mode =
+        internal::GetEnv("GOOGLE_CLOUD_CPP_SPANNER_TESTING_SESSION_MODE");
+    if (session_mode.has_value() && *session_mode == "multiplexed") {
+      options.set<spanner_experimental::EnableMultiplexedSessionOption>({});
+    }
+    client_ = std::make_unique<Client>(
+        MakeConnection(GetDatabase(), std::move(options)));
   }
 
   void SetUp() override {
 
@@ -19,7 +19,6 @@
 spanner_client_integration_tests = [
     "backup_extra_integration_test.cc",
     "backup_integration_test.cc",
-    "client_integration_test.cc",
     "client_stress_test.cc",
     "data_types_integration_test.cc",
     "database_admin_integration_test.cc",
 
@@ -0,0 +1,21 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# DO NOT EDIT -- GENERATED BY CMake -- Change the CMakeLists.txt file if needed
+
+"""Automatically generated unit tests list - DO NOT EDIT."""
+
+spanner_client_session_mode_sensitive_integration_tests = [
+    "client_integration_test.cc",
+]
@@ -252,7 +252,8 @@ using SessionPoolOptionList = OptionList<
     RouteToLeaderOption, SessionCreatorRoleOption, SessionPoolMinSessionsOption,
     SessionPoolMaxSessionsPerChannelOption, SessionPoolMaxIdleSessionsOption,
     SessionPoolActionOnExhaustionOption, SessionPoolKeepAliveIntervalOption,
-    SessionPoolLabelsOption>;
+    SessionPoolLabelsOption,
+    spanner_experimental::EnableMultiplexedSessionOption>;
 
 /**
  * Option for `google::cloud::Options` to set the optimizer version used in an