"Looks like Left 4 Dead's Survival mode will pit players against waves of raging zombies as part of new DLC, first announced last week. The upcoming add-on will also allow gamers to play Death Toll and Dead Air Versus campaigns along with the new Survival mode.
According to GameTrailers, Survival mode is akin to Call of Duty: World at War's Nazi Zombie mode, sending wave after wave of brain-eating monsters toward our favorite foursome. The mode will track how long players can survive the onslaught; however, it is unclear if players are competing as a team or for individual times. Survival will be playable on 12 maps -- since Valve has yet to announce new maps, Survival is likely to be played on 12 of the existing 20 maps in the game.
Left 4 Dead DLC will be made available online and, according to the video, in a special edition of the game coming this Spring."