Left 4 Dead 3’s existence may have been leaked directly from the source following a tour of Valve's Bellevue, Washington offices. Members of the Dota 2 Reddit community were visiting the studio to get a preview of annual Dota tournament The International when one attendee apparently snapped the picture above (enlarged by a NeoGAF member) of the studio’s internal changelog, which featured mentions of ‘LFD3’ and ‘Source 2’.
We emailed Valve to ask about the studio tour in question and the legitimacy of the photos supposedly taken there, but have yet to hear back from a company representative. Cooperative zombie survival FPS Left 4 Dead launched in 2008 on PC and Xbox 360, and was followed by Left 4 Dead 2 on the same platforms just the following year. We called the sequel “bigger, faster, nastier” and “the apocalypse to beat” in our Left 4 Dead 2 review:
Last November, Valve boss Gabe Newell confirmed that a next-gen Source engine existed and was just waiting for a game to roll it out with. The original Source engine runs everything from Half-Life 2 and Portal to Team Fortress 2 and Left 4 Dead. It was designed to be incrementally upgraded, which is why it's powered top-end games for so long.