Counter-Strike creator Minh 'Gooseman' Le claims to have first hand knowledge that Valve is working on Half-Life 3 and Left 4 Dead 3.
Speaking to GoRgnTV, Le suggested that, at this point, it is common knowledge that Valve is working on the sequels. He also said he's seen Half-Life 3 concept art.
"I don't think I can talk about that, to be honest, but I think it's kind of public knowledge, that people know that it is being worked on," he said. "And so if I were to say that yeah, I've seen some images, like some concept art of it, that wouldn't be big news to be honest.
"But yeah, I mean like 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."
Le also said he's "really excited" about "the new Left 4 Dead".
"I saw it, it looks great. I was really excited when I saw that, I was like 'wow, this looks great'. Because I really enjoyed Left 4 Dead, it was just one of those games that really just changed the industry. I think at the time there wasn't many good co-op games, so yeah, this is a great co-op game."
Valve has never publicly discussed Half-Life 3 since shipping Half-Life 2: Episode 2 in 2007. However, in 2013 a leak indicated that the core development team on Half-Life 3 includes some of Valve's most senior creators as well as a modder who built a Half-Life 2 spin-off.
In the same year, a group of Dota 2 players invited to tour Valve's offices also apparently spotted references to Left 4 Dead 3 and Source 2 projects listed on an internal changelog.
In June 2013, a fan site claimed to have acquired Half-Life 3 concept art from a "Valve employee". Of the 32 painted images, one showed key character Alyx Vance wearing Eli's jacket. The complete collection of supposed Half-Life 3 concept art can be seen here.