Index: src/wp-includes/default-filters.php
===================================================================
--- src/wp-includes/default-filters.php	(revision 45892)
+++ src/wp-includes/default-filters.php	(working copy)
@@ -521,6 +521,7 @@
 // Media
 add_action( 'wp_playlist_scripts', 'wp_playlist_scripts' );
 add_action( 'customize_controls_enqueue_scripts', 'wp_plupload_default_settings' );
+add_action( 'plugins_loaded', '_wp_add_additional_image_sizes', 0 );
 
 // Nav menu
 add_filter( 'nav_menu_item_id', '_nav_menu_item_id_use_once', 10, 2 );
Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 45892)
+++ src/wp-includes/media.php	(working copy)
@@ -1200,10 +1200,10 @@
 	 *
 	 * @since 4.4.0
 	 *
-	 * @param int   $max_width  The maximum image width to be included in the 'srcset'. Default '1600'.
+	 * @param int   $max_width  The maximum image width to be included in the 'srcset'. Default '2560'.
 	 * @param array $size_array Array of width and height values in pixels (in that order).
 	 */
-	$max_srcset_image_width = apply_filters( 'max_srcset_image_width', 1600, $size_array );
+	$max_srcset_image_width = apply_filters( 'max_srcset_image_width', 2560, $size_array );
 
 	// Array to hold URL candidates.
 	$sources = array();
@@ -4323,3 +4323,18 @@
 		'done' => $done,
 	);
 }
+
+/**
+ * Add additional default image sub-sizes.
+ *
+ * These sizes are added to `$_wp_additional_image_sizes`.
+ *
+ * @since 5.3.0
+ * @access private
+ */
+function _wp_add_additional_image_sizes() {
+	// 2x medium_large size
+	add_image_size( '1536x1536', 1536, 1536 );
+	// 2x large size
+	add_image_size( '2048x2048', 2048, 2048 );
+}