While the only actively supported version of WordPress is the most recent one, security updates are backported to older branches as a courtesy. All versions >=4.7 are in a security-only support state, receiving select security patches as a courtesy to users of WordPress.
The code maintained in the Gutenberg repository is just as critical to all WordPress versions >=5.0.
The code in the Gutenberg repository that corresponds to each release of WordPress is organized using wp/X.Y branches. These branches are frozen in time snapshots of the code that was used by wordpress-develop to build the final software that is released
