Back in February, Valve released the source code for Team Fortress 2 (TF2) into the Source SDK, which allows modders to see how it all works and get their standalone mods onto Steam. But also, it allows them to fix up issues directly in Team Fortress 2.
TF2 is free and has been for a while now. I don’t see valve turning that around this late in the lifespan of the game. As far as multiplayer online games go, TF2 is geriatric, amazing it still holds such a large playerbase.
Isn’t TF2 the last game in active development that’s still using Source 1? Dota was the first to switch to Source 2, CS switched a couple of years ago, and Deadlock is using it as well. Valve may touch up the older single player games like they did with HL1. L4D2 gets the occasional crash fix but nothing that constitutes actual development.
Actual open source might revitalize it.