The popular online zombie shooter Left 4 Dead from Valve gets a new downloadable content called "Survival Pack". Microsoft now confirmes the release on April 21. The expand content will be free of charge for both PC and Xbox 360 gamers. The Software Development Kit (SDK) will also follow this spring.

The upcoming L4D Survival Pack will add a new multiplayer game mode called, Survival, as well as two new campaigns for Versus Mode.
In the Survival mode 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. The Survival mode will be like the the zombie mode in Call of Duty: World at War.

Valve also said that a Critic's Choice Edition of the game will be in stores this spring. The Critic's Choice Edition will include all the content introduced in the L4D: Survival Pack as well as the original game.