Techradar has reported that ex-Valve employee and Counter Strike Co-creator, Ming Le, has confirmed that Half Life 3 and Left 4 Dead are being worked on right now. Half Life 3 has advanced into a more active stage than Left 4 Dead.
In a twitch interview, Ming Lee has said that he may have seen some concept art of the new series. He apparently seems to think that this is “public knowledge” and it is no big news if he confirms the making of Half Life 3
Le further said :
I guess I could say that I did see something that looked kinda like in the Half-Life universe, And I mean it wouldn’t surprise anyone if I said they’re doing it, they’re working on it, yeah. So to go on a limb I’d say I did see some concept art for Half-Life 3.
Regarding Left 4 Dead, he seemed pretty excited. He goes on to say
Valve is also busily working on as we speak. I saw it, it looks great. I was really excited when I saw that.