Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 39637)
+++ src/wp-includes/media.php	(working copy)
@@ -1069,12 +1069,21 @@
 
 	$image_basename = wp_basename( $image_meta['file'] );
 
+	/**
+	 * Filters the on/off behavior of responsive images when a GIF is used.
+	 *
+	 * @since 4.8.0
+	 *
+	 * @param bool $make_gifs_responsive Set this to true if you want all GIF images to have responsive srcset.
+	 */
+	$make_gifs_responsive = apply_filters( 'wp_calculate_image_srcset_gif', false );
+
 	/*
 	 * WordPress flattens animated GIFs into one frame when generating intermediate sizes.
 	 * To avoid hiding animation in user content, if src is a full size GIF, a srcset attribute is not generated.
 	 * If src is an intermediate size GIF, the full size is excluded from srcset to keep a flattened GIF from becoming animated.
 	 */
-	if ( ! isset( $image_sizes['thumbnail']['mime-type'] ) || 'image/gif' !== $image_sizes['thumbnail']['mime-type'] ) {
+	if ( $make_gifs_responsive || ! isset( $image_sizes['thumbnail']['mime-type'] ) || 'image/gif' !== $image_sizes['thumbnail']['mime-type'] ) {
 		$image_sizes[] = array(
 			'width'  => $image_meta['width'],
 			'height' => $image_meta['height'],