The boss of Valve - Gabe Newell has confirmed that the developer team is working on the next Source Engine which is leading to the next speculations list for upcoming games that could be in development.
On a question to Newell if they are working on new engine the answer from him was, “We’ve been working on new engine stuff for a while, we’ve just been waiting for a game to roll it out with.” When asked if this meant an entirely new engine and not just an extension of the existing one, he simply offered a “yeah.”
On that point we all ask ourselves what games may be in development from our favourite titles: Half-Life 3, Left 4 Dead 3, and Portal 3? On this question we can only speculate for now.
Earlier this year several references to a next generation Valve Source Engine were discovered in script files from the recently released Source Filmmaker version.
