The 'Survival Pack' downloadable content for Valve's cooperative zombie thriller Left 4 Dead will be released on April 21, Microsoft has confirmed.
Valve's zombie shooter is expanding for the first time with the upcoming 'Survival Pack', which will add a new Survival mode where players attempt to survive endless hordes of zombies on at least 12 maps, and allow the Dead Air and Death Toll campaigns to be played in the multiplayer Versus mode.
Valve has previously confirmed that the add-on pack will be available free of charge for both PC and Xbox 360 gamers, hopefully simultaneously. A Critic's Choice Edition of the game will hit retail stores at the same time, offering the original game plus access to all the content introduced in the Survival Pack.
Also, the Software Development Kit (SDK) for the game is expected this spring as well, allowing players to create their own custom content, campaigns and levels for the game.