Index: src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php
===================================================================
--- src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(revision 44725)
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php	(working copy)
@@ -1715,6 +1727,7 @@
 			$links['replies'] = array(
 				'href'       => $replies_url,
 				'embeddable' => true,
+				'count' => wp_count_comments(),
 			);
 		}