Valve announced today that they will release the upcoming Dead Air DLC for Left 4 Dead 2 early, or on July 22 at the latest, thanks to a community challenge by the developer. The challenge was for 20,000 players to get the “Stream Crosser” achievement, which the community accomplished in less than five hours.
The Dead Air Campaign, which was in the original Left 4 Dead, is part of the Cold Stream DLC, which is releasing later. Valve says that they will try to release Dead Air early depending on how long testing will go, but you can at least expect to play Dead Air by July 22. The DLC will be available for PC and Xbox 360.
Source: Valve
