Valve is working on Left 4 Dead 3, at least according to a leaked entry found on the Steamworks developer website that mentions the new zombie game.
Valve is currently working on getting Dota 2 ready for its public release and on continuously updating existing games like Counter-Strike: Global Offensive. It's also creating different projects like the Steam Box mini-PC.
The company recently opened up the Steamworks API to all, and apparently a listing for Left 4 Dead 3 has been found within the service's registries.
The leak, coming via NeoGAF, mentions the new iteration in the zombie shooter franchise, but no other details are available. Apparently, it hasn't been updated in some time, hinting that the project is currently on hold.
Valve has made no statement concerning Left 4 Dead 3's leak and, seeing as how it won't be coming to E3 2013, it's unlikely that the title will be showcased to the world next week.