Re: SiN Episodes Fan Questions Answered
First, I think we need to seperate the toolset and the SDK.
The toolset is what is used to create assets. Tools like Hammer, HLMV and Faceposer all belong to the toolset. We use slightly modified versions of these tools when creating the levels, although if we release our FGD, there shouldn't be any problem for you to use those tools.
However, the SDK is the code used to create the gameplay associated with the engine. When I say that the number of differences between the two is bordering on the extreme, I'm not bullshitting you. In addition, we've modified parts of Source itself to add functionality.
So to reiterate: Shared toolset, yes. Shared SDK, not likely.