Microsoft announced today that the Left 4 Dead Survival Pack DLC will be released on Xbox Live on April 21. While this applies to the Xbox 360 version, Valve previously mentioned that the DLC would also be available on PC starting April 21.

The free pack adds the new Survival game mode where players have to fend hordes of increasing zombies in an attempt to survive as long as possible. There will be 12 new maps, with 11 being sections of existing levels and one created especially for Survival mode – Lighthouse.

It also adds Versus mode to the final two co-op campaigns – Dead Air and Death Toll.