Valve's Gabe Newell had an AMA today in the quasi-satirical r/The_Gaben subreddit. During his brief session answering community questions, Newell revealed that Valve might actually still be a game developer.

Who knew?

Reddit user Baldemoto asked that which should not be asked to Newell. His response will shock you (assuming you missed the headline that you clicked on to read this news piece).
Is Valve still working on any fully-fledged single player games?An unidentified anonymous source at Valve has said that Half Life 3 has been cancelled. Is that source legitimate? The number 3 must not be said. Yes. I personally believe all unidentified anonymous sources on the Internet. 20-30. Same as always. We're adding servers all the time.

There you go. Valve is apparently working on a "fully-fledged single player" game. Of course, that could very well mean it's a full-fledged single player VR game since that seems to be the new hotness at Valve that doesn't end in -ota 2.

What about Source 2? Reddit user The_Four_Leaf_Clover asked that very question today.
The_Four_Leaf_Clover: Does Valve plan on doing anything with Source 2 in the coming years? If so, what?

We are continuing to use Source 2 as our primary game development environment. Aside from moving Dota 2 to the engine recently, we are are using it as the foundation of some unannounced products. We would like to have everyone working on games here at Valve to eventually be using the same engine. We also intend to continue to make the Source 2 engine work available to the broad developer community as we go, and to make it available free of charge.

So, Valve is working on a "fully-fledged single player" game and the studio is using Source 2 as their primary game development environment? I'm starting to believe that Valve does indeed still make games. Could it still be a VR game? Possibly. However, it was said a while back that Valve has moved their VR development mainly over to Unity.

Alright, but what about Counter-Strike: Global Offensive? Well, there wasn't too much on that front. What did he say about Dota 2? Well, we found out that Dota 2 is Newell's favorite multiplayer game. And Half-Life Portal 2 is his favorite single-player game of theirs. Uh, sorry Half-Life fans. Maybe don't get your hopes up too high for that unannounced "fully-fledged single player" game to be Half-Life 3. To his credit, Gabe Newell did explain why he prefers Portal to Half-Life.
The issue with Half-Life for me is that I was involved in a much higher percentage of the decisions about the games, so it's hard for me to look at them as anything other than a series of things I regret. There's no information in my response about what we'll do in the future. It's simply easier for me to be a fan of things that in which I was less directive.(...)

If you are involved in a game, everything ends up being a set of trade-offs. Anything in a game is a sacrifice of things not in the game. I just feel those more personally about Half-Life for a bunch of reasons.
And Xen.

Poor Xen.

It does seem like we might see more Left 4 Dead in the future. Here is what he had to say when asked if they would continue the Left 4 Dead series.
Products are usually the result of an intersection of technology that we think has traction, a group of people who want to work on that, and one of the game properties that feels like a natural playground for that set of technology and design challenges.

When we decided we needed to work on markets, free to play, and user generated content, Team Fortress seemed like the right place to do that. That work ended up informing everything we did in the multiplayer space.

Left 4 Dead is a good place for creating shared narratives.

Finally, the big question was asked about what needs to improve with Steam. His response? "Support." Of course, this has been said by various Valve employees for years now. Let's hope they turn things around in 2017.

Also, don't get your hopes up for Valve's "fully-fledged single player" game. You should know better by now. With Valve, they could scrap the entire idea entirely tomorrow without even a hint as to what it might have been.