The next Garry's Mod update is coming soon.
The current plan is to release the next Garry's Mod update on 13th of March at 4PM GMT.
This update will be backwards compatible with existing servers, so servers do not need immediate updating and players can still join old servers, but it is still highly recommended to update as soon as the update releases to get all the new features and fixes.
You can preview the list of upcoming changes here:
(Please note this list is still work in progress and is subject to change.)
For more details, please see the Steam Announcement: