Extend Woocommerce rest api routes fails

While I’m trying to extend Woocommerce Rest-API routes with a custom one I face the following problem. I have the following class which tries to hook inside Woocommerce API

class API_LOADER
{
public function init()
        {
            add_action( 'woocommerce_api_loaded', array( $this, 'load' ) );
        }
        public function load()
        {
            //This method will be not called
            require_once plugin_dir_path( __FILE__ ).'wc-api-custom.php';
            add_filter( 'woocommerce_api_classes', array( $this, 'register' ) );
        }
} 

but woocommerce_api_loaded will not trigger any callback.

What I do wrong in this case