Update: The content is now available for the PC as well.
Original: Valve’s Doug Lombardi just shot over a message saying the free Left 4 Dead Survival Pack will be released on Xbox Live at around 2 am PST on April 21, which should be in just around 8 hours or so. The PC version will arrive later in the day.
The DLC will be available for free and brings with it a new Survival multiplayer mode and two complete Versus Mode campaigns. For some more details on the DLC, check our post on it here.