Via [url=https://list.valvesoftware.com/]HLDS[/url]:

[quote=Valve][b]Happy Smissmas 2018![/b]
- All players who play TF2 during the event will receive a Stuffed Stocking as a gift! Stockings contain goodies for good little Mercenaries.
- Event runs through January 7th, 2019
- Added the Winter 2018 Cosmetic Case
- Contains 18 new community-contributed items
- The Festivizer can be found as a bonus drop when opening the case
- Mann Co. Store winter sale!

[b]General[/b]
- Fixed func_rotating entity not working properly in maps like 2Fort and Gravelpit
- Fixed Strange Filter: Brimstone not displaying the prefix in the weapon name
- Fixed a Mann vs. Machine bug with giant robots reported by Justin G. (sigsegv)
- Added LAN Downunder 2018 tournament medals
- Added ETF2L 6v6 Season 31 and Highlander Season 17 tournament medals
- Added Brazil Fortress Season 3 tournament medals
- Added Russian Highlander Season 1 tournament medals
- Added Sacred Scouts 6v6 tournament medals
- Added AsiaFortress Cup Season 14 tournament medals
- Added AsiaFortress LAN 2018 tournament medals
- Updated the Starstorm Slumber unusual effect to fix a display problem
- Updated the backpack image for Mr. Quackers
- Updated pd_monster_bash
- Fixed an out-of-bounds exploit in RED's courtyard
- Updated pl_millstone_event
- Fixed a spot where players could trap players with teleport exit
- Fixed Headless Horseman getting stuck in B area house staircase
- Updated p_snakewater_final1
- Fixed "splash bug" issues throughout the map
- Fixed a lot of visual issues
- Improved clipping and made movement smoother
- Made fence near yard closed to projectiles[/quote]

Rumor has it:

- Are you confused about the MvM robot bug fix? There's much more to it than meets the eye, so [url=https://www.reddit.com/r/tf2/comments/a7s759/tf2_update_for_121918_122018_utc_smissmas_2018/ec5ecvy/?context=1]sit down for a fireside chat all about it[/url] while you get comfortable next to /u/sigsegv__

- Don't forget to drink up on your daily dose [url=https://github.com/SteamDatabase/GameTracking-TF2/commit/1a509a24ae8ae5036809af2a3d3e04e5c60467c2]of localization files[/url], made possible in part by contributions from [url=https://translation.steampowered.com/]Translators Like You - Thank You[/url]

- This update ends a 49 day long drought without any updates, tying the record for longest drought which was set earlier in the year with a stretch without an update from 8/2/18 (8/3/18 UTC) to 9/21/18 (9/22/18 UTC)

- Size is ~120 MB

------------------------

[b][url=https://support.steampowered.com/kb_article.php?ref=1558-AFCM-4577]Valve will end its support of Steam on Windows XP and Windows Vista in two weeks, on 1/1/19.[/url] Additionally, [url=https://support.steampowered.com/kb_article.php?ref=5953-QTIO-1764]Valve is also ending its support of Steam on Mac OS X Lion, Mountain Lion, Mavericks, and Yosemite on 1/1/19 as well.[/url][/b] Any future TF2 updates that moves the minimum Steam client version beyond the last one available for XP/Vista will render it unplayable unless you upgrade Windows. Any future TF2 updates that moves the minimum Steam client version beyond the last one available for Lion through Yosemite will also render it unplayable unless you grab Mac OS X El Capitan or newer from the Mac App Store.