Valve has confirmed that its Source Engine SDK and modding tools will now be available for free, following the F2P re-release of Team Fortress 2.
The engine and mod kit was previously available with the purchase of a game, but after a loophole was pointed out on Rock, Paper, Shotgun that meant the tools would still be available with the free TF2, Valve’s Robin Walker confirmed that the engine was now going to be given away for free.
"We are in the process of getting it all done. It’s a bit messy because we have multiple versions of the SDK, and there’s some dependencies we need to shake out,” he explained.”
“But yes, the gist of it is that we’re just going to go ahead and make the Source SDK freely available."