Interesting, Gabe Newell over at Valve posted on Reddit that they are working on a new single player game. He also mentioned that there is a possibility within the Half-life and Portal segment to see some new games.
Everybody is still hoping for Half-Life 3, but that question remains unanswered. Valve will keep using their Source Engine 2 game render engine for the games as foundation for the unannounced games. below a recap of the answers:
Hello Mr. Newell,
What is the status of Half Life 3/Half Life 2 Episode 3?
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?
How many people are now working on CS:GO? The community is frustrated at the lack of updates and the fact that most of the bugs haven't been fixed.
How long will it be until Valve adds CS:GO servers in other parts of the world (such as Russia)?
Valve is working on a new single player game