Back when Alien Swarm got released last year, many thought this would mean the Source SDK would become freely available to all. But that wasn’t to be, as Alien Swarm used its own, specialized mod tools.
Now TF2 has gone free-to-play. The way it works is – going premium will give you access to the Source SDK. That means any purchase from the Mann Co Store, as tiny as it could possibly be, will give you access to the Source SDK.
But apparently, there has been a change in plans!