add_action( 'save_post', function( $post_id ) {
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
    return;
  }

  $transient_id = TRANSIENT_AMP_PREFIX . $post_id;
  $transient_file = get_theme_amp_cache_path() . $transient_id;
  if ( file_exists( $transient_file ) ) {
    wp_filesystem_delete( $transient_file );
    delete_db_cache_records( $transient_id );
  }
});