443 volunteers contributed to this release, lead by Mel Choyce and Weston Ruter. At the time of writing this, WordPress 4.9 has been out for about 17 hours, and has already been downloaded 2,075,053 times!
All users can safely update from Dashboard -> Updates or download and update manually, though you should probably backup first just in case, unless you’re already using VaultPress, which you really should be.
WordPress 5.0 is next, and it sounds like the promised fully rebuilt editor is still on schedule. If you want to try it out or contribute to its development, please feel free to start with the Gutenberg plugin.