Left 4 Dead 3 may be in development, according to a photo allegedly taken of a Valve developer's monitor by a member of a Dota 2 subreddit tour group that went through the company's offices.
Reddit user r_dageek posted the photo on the Dota 2 subreddit, pointing out that the image displays references to Source Engine 2 and Left 4 Dead 3, as well as a change log for a new Dota 2 quest. A zoomed-in image provided by CyborgMatt, seen below, shows text with a timestamp of Aug. 5 stating "[Source2] Restored L4D3's devtest unit test. Ran locally 6 times without an assert. There may be so..."
Source 2 refers to the successor of Valve's Source engine, which co-founder Gabe Newell confirmed the existence of back in November during a Q&A session with members of 4chan's /v/ board.
In an interview with Eurogamer last year, Valve's writer Chet Faliszek said "some time down the road" when asked if they'll do another Left 4 Dead, following up with "like anything, I would say that to all of our games. So that's not a promise of when or where."
We've reached out to Valve for comment.