Via the CS:GO blog:

MISC

• Fixed possible remote code execution bug in KeyValues parsing. Thanks to xPaw for finding and reporting the issue!
• Fixed a bug allowing community servers to override certain game files.
• Added support in vbsp for clip brush textures with different material types.
• Added CS:GO in-game blog localization for Finnish.
• Significantly reduced holiday cheer.
• Added convars cl_weapon_debug_show_accuracy and cl_weapon_debug_show_accuracy_duration
  • With “cl_weapon_debug_show_accuracy 1,” when a shot is fired, a 12 inch circle will be drawn at the Effective Range of the weapon, i.e, the farthest distance at which the shot is guaranteed to fall within a 12 inch circle.
  • With “cl_weapon_debug_show_accuracy 2,” when a shot is fired, a circle will be drawn at the surface that is aimed at showing the area that could have been hit by the bullet given its inaccuracy.
  • cl_weapon_debug_show_accuracy_duration ( default 10 ) determines how long the debug circles last.
  • The further the shot is into the spray sequence, the more red the circle will be.

AUDIO

• Increased radius of c4 disarm sound
• Fixed some cases where alt-tabbing away and back to the game would cause incorrect sounds to play

MAPS

Cache

• Visibility improvements based on color-blind player feedback
• Texture improvements
• New vent models
• Added subtle markers for grenade throws (thanks James Bardolph)
• Added plant-zone decals to Bombsite B
• Added graphic for “Sun-room” (thanks Thurnip)
• Fixed fade distance on crate in checkers
• Fixed weapons being irretrievable under vent
• Fixed all known bomb-stuck spots
• Fixed an exploit involving flashbangs from mid into checkers
• Fixed pixelwalks at mid, T-Spawn, A main, A site
• Improved .nav mesh (thanks p_NM)

Nuke

• Improved accuracy of grenade clips on metal containers
• Clip brushes now play the correct material type footstep sound
• Performance optimizations
• Removed crate stack from CT side
• Removed railings outside HUT
• Removed railings at top of Heaven ladder
• Lowered ambient soundscape volumes
• Door opening and closing predictability fixed
• Improved .nav mesh (thanks Bez)
• Fixed +use interaction through tool or clip brushes
• Fixed double doors being blocked by their sibling door being blocked by the player

Rumor has it:

• A previous version branch titled "13532" was made available, this branch matches the state of the game from the last update

  • If you need to or want to use this branch, right-click on CS:GO in Steam, click "properties", go to the "betas" tab, and select the "13532" branch
  • Be aware however that you'll have very limited access to things, and you won't be able to play Valve matchmaking of any sort
  • If you're a server operator or a league/tournament admin that wishes to play on the previous version, use "+app_update 740 -beta 13532" in SteamCMD

• More shenanigans involving chickens, the death message added last update now also says: "She was yours for <x> seconds."

• Low level changes, VPK contents changes, and script changes oh my! Low-level changes, VPK contents changes and... https://github.com/SteamDatabase/GameTracking/commit/c690d2144312491118dd8a432426053cb70e343a

• Size is ~110 MB