diff --git a/includes/Core/Authentication/Clients/OAuth_Client.php b/includes/Core/Authentication/Clients/OAuth_Client.php
index b600d844dce..636cd18f076 100644
--- a/includes/Core/Authentication/Clients/OAuth_Client.php
+++ b/includes/Core/Authentication/Clients/OAuth_Client.php
@@ -569,24 +569,6 @@ public function refresh_profile_data( $retry_after = 0 ) {
 		}
 	}
 
-	/**
-	 * Determines whether the authentication proxy is used.
-	 *
-	 * In order to streamline the setup and authentication flow, the plugin uses a proxy mechanism based on an external
-	 * service. This can be overridden by providing actual GCP credentials with the {@see 'googlesitekit_oauth_secret'}
-	 * filter.
-	 *
-	 * @since 1.0.0
-	 * @deprecated 1.9.0
-	 *
-	 * @return bool True if proxy authentication is used, false otherwise.
-	 */
-	public function using_proxy() {
-		_deprecated_function( __METHOD__, '1.9.0', Credentials::class . '::using_proxy' ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
-
-		return $this->credentials->using_proxy();
-	}
-
 	/**
 	 * Determines whether the current owner ID must be changed or not.
 	 *
diff --git a/tests/phpunit/integration/Core/Authentication/Clients/OAuth_ClientTest.php b/tests/phpunit/integration/Core/Authentication/Clients/OAuth_ClientTest.php
index f265b53c30a..29778b7be9f 100644
--- a/tests/phpunit/integration/Core/Authentication/Clients/OAuth_ClientTest.php
+++ b/tests/phpunit/integration/Core/Authentication/Clients/OAuth_ClientTest.php
@@ -709,23 +709,6 @@ function ( Request $request ) {
 		$this->assertTrue( $google_client_mock->shouldDefer() );
 	}
 
-	public function test_using_proxy() {
-		$this->setExpectedDeprecated( OAuth_Client::class . '::using_proxy' );
-		$context = new Context( GOOGLESITEKIT_PLUGIN_MAIN_FILE );
-		$client  = new OAuth_Client( $context );
-
-		// Use proxy by default.
-		$this->assertTrue( $client->using_proxy() );
-
-		// Don't use proxy when regular OAuth client ID is used.
-		$this->fake_site_connection();
-		$this->assertFalse( $client->using_proxy() );
-
-		// Use proxy when proxy site ID is used.
-		$this->fake_proxy_site_connection();
-		$this->assertTrue( $client->using_proxy() );
-	}
-
 	public function test_get_proxy_permissions_url() {
 		$context = new Context( GOOGLESITEKIT_PLUGIN_MAIN_FILE );