Left 4 Dead 3 and Source 2 were spotted by members of the Dota 2 subReddit during a recent tour of Valve's Seattle office.
During the tour a picture was taken of an internal change log, which mentions Left 4 Dead 3 and Source 2. NeoGAF user "CyborgMatt" produced a zoomed in version, which shows the interesting part in all its glory.
The appearance of Source 2 - the second iteration of Valve's own game engine - comes as no surprise. Back in November 2012 Valve chief Gabe Newell confirmed the company was working on a new game engine.
"We've been working on Valve's new engine stuff for a while, we're probably just waiting for a game to roll it out with," Newell said at the time.
Is that game Left 4 Dead 3?
In October 2012, Eurogamer asked Valve's Chet Faliszek if he'd like to make a third game in the co-op zombie shooter. "You know, some time down the road," he replied. "Like anything, I would say that to all of our games. So that's not a promise of when or where."
But would you like to? we pressed.
"I really love working on that series. It's one of my favourite series. It's just so much fun with the characters and the world. I love zombies and I love horror. So, yeah."
The original Source engine debuted with Counter-Strike: Source and Half-Life 2 in 2004.