diff --git a/src/GapicClientTrait.php b/src/GapicClientTrait.php
index a8dd6782a..ace0d621f 100644
--- a/src/GapicClientTrait.php
+++ b/src/GapicClientTrait.php
@@ -80,6 +80,7 @@ trait GapicClientTrait
         Call::CLIENT_STREAMING_CALL => 'startClientStreamingCall',
         Call::SERVER_STREAMING_CALL => 'startServerStreamingCall',
     ];
+    private bool $isNewClient;
 
     /**
      * Initiates an orderly shutdown in which preexisting calls continue but new
@@ -385,6 +386,12 @@ private function setClientOptions(array $options)
             $options['restVersion'] = Version::getApiCoreVersion();
         }
 
+        // Set "client_library_name" depending on client library surface being used
+        $userAgentHeader = sprintf(
+            'gcloud-php-%s/%s',
+            $this->isNewClientSurface() ? 'new' : 'legacy',
+            $options['gapicVersion']
+        );
         $this->agentHeader = AgentHeader::buildAgentHeader(
             $this->pluckArray([
                 'libName',
@@ -392,6 +399,8 @@ private function setClientOptions(array $options)
                 'gapicVersion'
             ], $options)
         );
+        $this->agentHeader['User-Agent'] = [$userAgentHeader];
+
         self::validateFileExists($options['descriptorsConfigPath']);
         $descriptors = require($options['descriptorsConfigPath']);
         $this->descriptors = $descriptors['interfaces'][$this->serviceName];
@@ -469,6 +478,14 @@ private function createTransport(
         $configForSpecifiedTransport['clientCertSource'] = $clientCertSource;
         switch ($transport) {
             case 'grpc':
+                // Setting the user agent for gRPC requires special handling
+                if (isset($this->agentHeader['User-Agent'])) {
+                    if ($configForSpecifiedTransport['stubOpts']['grpc.primary_user_agent'] ??= '') {
+                        $configForSpecifiedTransport['stubOpts']['grpc.primary_user_agent'] .= ' ';
+                    }
+                    $configForSpecifiedTransport['stubOpts']['grpc.primary_user_agent'] .=
+                        $this->agentHeader['User-Agent'][0];
+                }
                 return GrpcTransport::build($apiEndpoint, $configForSpecifiedTransport);
             case 'grpc-fallback':
                 return GrpcFallbackTransport::build($apiEndpoint, $configForSpecifiedTransport);
@@ -1051,4 +1068,12 @@ protected function modifyStreamingCallable(callable &$callable)
     {
         // Do nothing - this method exists to allow callable modification by partial veneers.
     }
+
+    /**
+     * @internal
+     */
+    private function isNewClientSurface(): bool
+    {
+        return $this->isNewClient ?? $this->newClient = substr(__CLASS__, -10) === 'BaseClient';
+    }
 }
diff --git a/tests/Tests/Unit/GapicClientTraitTest.php b/tests/Tests/Unit/GapicClientTraitTest.php
index 3c98429e4..9c2f5f756 100644
--- a/tests/Tests/Unit/GapicClientTraitTest.php
+++ b/tests/Tests/Unit/GapicClientTraitTest.php
@@ -872,7 +872,7 @@ public function setClientOptionsData()
         }
         $expectedProperties = [
             'serviceName' => 'test.interface.v1.api',
-            'agentHeader' => AgentHeader::buildAgentHeader([]),
+            'agentHeader' => AgentHeader::buildAgentHeader([]) + ['User-Agent' => ['gcloud-php-legacy/']],
             'retrySettings' => $expectedRetrySettings,
         ];
         return [
@@ -1356,7 +1356,8 @@ public function testUserProjectHeaderIsSetWhenProvidingQuotaProject()
                 $this->isInstanceOf(Call::class),
                 $this->equalTo([
                     'headers' => AgentHeader::buildAgentHeader([]) + [
-                        'X-Goog-User-Project' => [$quotaProject]
+                        'X-Goog-User-Project' => [$quotaProject],
+                        'User-Agent' => ['gcloud-php-legacy/']
                     ],
                     'credentialsWrapper' => $credentialsWrapper
                 ])
@@ -1718,6 +1719,25 @@ public function testMtlsClientOptionWithDefaultClientCertSource()
         $this->assertTrue(is_callable($options['clientCertSource']));
         $this->assertEquals(['foo', 'foo'], $options['clientCertSource']());
     }
+
+    public function testSurfaceAgentHeaders()
+    {
+        // V1 does not contain new headers
+        $client = new GapicClientTraitRestOnly([
+            'gapicVersion' => '0.0.2',
+        ]);
+        $agentHeader = $client->getAgentHeader();
+        $this->assertStringContainsString(' gapic/0.0.2 ', $agentHeader['x-goog-api-client'][0]);
+        $this->assertEquals('gcloud-php-legacy/0.0.2', $agentHeader['User-Agent'][0]);
+
+        // V2 contains new headers
+        $client = new GapicV2SurfaceClient([
+            'gapicVersion' => '0.0.1',
+        ]);
+        $agentHeader = $client->getAgentHeader();
+        $this->assertStringContainsString(' gapic/0.0.1 ', $agentHeader['x-goog-api-client'][0]);
+        $this->assertEquals('gcloud-php-new/0.0.1', $agentHeader['User-Agent'][0]);
+    }
 }
 
 class GapicClientTraitStub
@@ -1884,6 +1904,11 @@ private static function defaultTransport()
     {
         return 'rest';
     }
+
+    public function getAgentHeader()
+    {
+        return $this->agentHeader;
+    }
 }
 
 class GapicClientTraitOperationsStub extends GapicClientTraitStub
@@ -1902,3 +1927,38 @@ public function getOperation($name, $arg1, $arg2)
     {
     }
 }
+
+class GapicV2SurfaceBaseClient
+{
+    use GapicClientTrait;
+
+    public function __construct(array $options = [])
+    {
+        $clientOptions = $this->buildClientOptions($options);
+        $this->setClientOptions($clientOptions);
+    }
+
+    public static function getClientDefaults()
+    {
+        return [
+            'apiEndpoint' => 'test.address.com:443',
+            'serviceName' => 'test.interface.v1.api',
+            'clientConfig' => __DIR__ . '/testdata/test_service_client_config.json',
+            'descriptorsConfigPath' => __DIR__.'/testdata/test_service_descriptor_config.php',
+            'transportConfig' => [
+                'rest' => [
+                    'restClientConfigPath' => __DIR__.'/testdata/test_service_rest_client_config.php',
+                ]
+            ],
+        ];
+    }
+
+    public function getAgentHeader()
+    {
+        return $this->agentHeader;
+    }
+}
+
+class GapicV2SurfaceClient extends GapicV2SurfaceBaseClient
+{
+}