Index: src/wp-includes/class-wp-site-query.php
===================================================================
--- src/wp-includes/class-wp-site-query.php	(revision 41909)
+++ src/wp-includes/class-wp-site-query.php	(working copy)
@@ -211,7 +211,8 @@
 	 * @since 4.6.0
 	 *
 	 * @param string|array $query Array or URL query string of parameters.
-	 * @return array|int List of WP_Site objects, or number of sites when 'count' is passed as a query var.
+	 * @return array|int List of WP_Site objects, a list of site ids when 'fields' is set to 'ids',
+	 *                   or the number of sites when 'count' is passed as a query var.
 	 */
 	public function query( $query ) {
 		$this->query_vars = wp_parse_args( $query );
@@ -224,7 +225,8 @@
 	 *
 	 * @since 4.6.0
 	 *
-	 * @return array|int List of WP_Site objects, or number of sites when 'count' is passed as a query var.
+	 * @return array|int List of WP_Site objects, a list of site ids when 'fields' is set to 'ids',
+	 *                   or the number of sites when 'count' is passed as a query var.
 	 */
 	public function get_sites() {
 		$this->parse_query();
Index: src/wp-includes/ms-blogs.php
===================================================================
--- src/wp-includes/ms-blogs.php	(revision 41909)
+++ src/wp-includes/ms-blogs.php	(working copy)
@@ -636,7 +636,8 @@
  *                                           Default empty array.
  *     @type bool         $update_site_cache Whether to prime the cache for found sites. Default true.
  * }
- * @return array|int List of sites, or number of sites when 'count' is passed as a query var.
+ * @return array|int List of WP_Site objects, a list of site ids when 'fields' is set to 'ids',
+ *                   or the number of sites when 'count' is passed as a query var.
  */
 function get_sites( $args = array() ) {
 	$query = new WP_Site_Query();