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Valve's Left 4 Dead Survival Pack DLC will be released on Xbox 360 on April 21, Microsoft has just confirmed.

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The pack includes the new survival mode, which challenges players to hold out against a never ending wave of infected for as long as possible, as well as the addition of the Dead Air and Death Toll campaigns in Versus mode.

Valve has previously said that the DLC pack will be released on Xbox 360 and PC simultaneously, so we'd say it's a fair bet that mouse and keyboard gamers will see the add-on on the same date.