Taken from here.
Gabe Newell: We’ve been working on Valve’s new engine stuff for a while, we’re probably just [incomprehensible, subtitled as: “waiting for a game to roll it out with”]
Fan: Is it going to be more than just an extension to Source? Is it an entirely new engine?
Gabe Newell: Yeah!
Hmmmmmm… Episode 3 anyone? 😛