Valve hands Team Fortress 2 source code to modders

Mod makers rejoice: The Team Fortress 2 SDK has arrived! We've updated the Source SDK with all of TF2's client and server game code. Change, extend, or rewrite TF2, and publish them as mods ...
"We're already preparing for the porting efforts and a potential Steam release now that we've been legally enabled to pursue ...
In typical fashion, Valve just made the Team Fortress 2 client and server game code public without much fanfare. However, this move has the potential to make a huge impact on the 17-year-old ...