Left 4 Dead DLC hits April 21

Today Valve detailed the contents of Left 4 Dead’s Survival Pack, which arrives Tuesday of next week on PC and Xbox 360.

The Survival Pack, which is free, adds a new Survival Mode, where players must survive increasingly frequent waves of zombies across 12 maps. According to Valve, it is almost impossible to survive for more than 14 minutes due to the fact that by that time in the game Tanks spawn every 14 seconds.

According to Kerry Davis and Scott Dalton, two employees at Valve, “Given the extreme pace of Survival Mode, the number of zombies killed in a single round often outnumbers an entire campaign.”

Aside from Survival Mode, the DLC adds the Dead Air and Death Toll campaigns to Versus mode.

Read: Left 4 Dead Survival Pack DLC Hits PC Next Week.