Valve have just updated the Source 1 SDK on GitHub to the latest code based on Team Fortress 2, effectively making TF2 code source available.
SDK was previously updated in 2014.
Remember that this does not include the source engine which is still closed source, good for modding but you won’t be able to do crazy ports or anything anytime soon.
Remember that this does not include the source engine which is still closed source, good for modding but you won’t be able to do crazy ports or anything anytime soon.