Index: src/wp-includes/rest-api.php
===================================================================
--- src/wp-includes/rest-api.php	(revision 46542)
+++ src/wp-includes/rest-api.php	(working copy)
@@ -588,9 +588,9 @@
 		header( 'Access-Control-Allow-Origin: ' . $origin );
 		header( 'Access-Control-Allow-Methods: OPTIONS, GET, POST, PUT, PATCH, DELETE' );
 		header( 'Access-Control-Allow-Credentials: true' );
-		header( 'Vary: Origin' );
+		header( 'Vary: Origin', false );
 	} elseif ( ! headers_sent() && 'GET' === $_SERVER['REQUEST_METHOD'] && ! is_user_logged_in() ) {
-		header( 'Vary: Origin' );
+		header( 'Vary: Origin', false );
 	}

 	return $value;