Team Fortress 2 Classic is coming to Steam thanks to Valve adding TF2 to the Source SDK

Team Fortress 2 Classic, a mod that aims to re-imagine the early post-launch era of Team Fortress 2, will be released on Steam.

Recently we had the news that Valve had effectively made Team Fortress 2 "Source Available", as it's now part of the Source SDK. In the announcement Valve said developers would be able to release their mods on Steam, and so it's happening. A new Team Fortress 2 Classic Steam page has been put up, although there's no date listed on it other than 2025.

More about it from the Steam page:

Team Fortress 2 Classic is a mod for Team Fortress 2 that re-imagines the early post-launch era — circa 2008 to 2009 — of the original game. Starting from there, we've added quality-of-life features, remade and reworked scrapped content, and built onto it with full-size updates in homage to TF2's timeless style and tone.

NEW-OLD FEATURES

• Meet the Civilian, a brand-new special class based on the legacy Team Fortress Classic character, and deliver him mostly-unharmed to the objective in VIP mode.
• Use TF2 prerelease-inspired weapons like the Nailgun, the Dynamite Pack, and the Tranquilizer Gun, all redesigned from the ground up to feel right at home with what's already there.
• Go on a rampage in Four-Team matches, where GRN and YLW bring their unique (yet strangely identical) brand of violence to Arena, King of the Hill, and more.

NEW-NEW FEATURES

• Exclusive new gamemodes, including Domination, Territorial Domination, and VIP Race — all playable on professional-quality official maps, with more yet to come.
• Jump pads, flak cannons, bricks, chains wrapped around your fists; made-in-house weapons that go beyond mere sidegrades, and dramatically change how you play the game.
• Extensive modding support, allowing players to customize the look of their game, and allowing servers to host advanced custom weapon packs and maps.
• A whole host of visual enhancements, including improved textures, models, mapping features, and restored toon-style shading that was mostly absent in the retail release.
• A chicken, or so we're led to believe.

The developers of the mod likely have to port over their changes to the newer SDK, so it may still be a while until the Steam release is available.