Valve: “Mod makers, rejoice! We’ve just released a massive update to the Source SDK, adding all the Team Fortress 2 client and server game code. This update will allow content creators to build completely new games based on TF2. We’re also doing a big update to all our multiplayer back-catalogue Source engine titles (TF2, DoD:S, HL2:DM, CS:S, and HLDM:S), adding 64-bit binary support, a scalable HUD/UI, prediction fixes, and a lot of other improvements!”
Source: N4G PC The TF2 SDK has arrived