It's CHRISTMAS UPDATE time
You'll get a trail of gifts to open and play with, and also four new accessories - santa hat, bottle, rattle, and a teddy bear.
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 3425132 · beta branch
Steam updated · First observed
Build 3425132 · public branch
Steam updated · First observed