This update allows users to play an optional Christmas mode, where there is a new music track added, snow, and seasonal pickups. It will be available through January 12th.
There are also various other minor patches & fixes.
Patch Notes for December 7th Release
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 10102826 · public branch
Steam updated · First observed