The plan is to release Gutenberg in WordPress core with the release of the Version 5.0. WordPress 5.0 is a major release and the roll-out will not happen automatically. Companies offering managed WordPress hosting will test the new release for a period of time before they upgrade clients' sites to the version. If you feel for any reason, that your site won't be ready for Gutenberg yet, you can install the plugin called Classic Editor to keep the current editor running on your site. For more granular control over which content and post type is edited with Gutenberg, you'll find 16 Methods to avoid Gutenberg editor, when it becomes available in WordPress 5.0