 The two full campaigns of "Death Toll" and "Dead Air" for versus mode—which were previously unavailable—are included, as well as the survival game mode, where the survivors try to survive endless waves of the infected for as long as possible.On February 11, 2009, Valve announced that the downloadable content for the game would be free for both the Xbox 360 and PC; and on April 21, it was released.Survival mode shipped with 16 maps, 15 of them being modified portions of existing maps and one being a new lighthouse-themed level titled "The Last Stand".