Valve made a big announcement for the very popular Left 4 Dead today, with a planned update due for release within the next few months. The update, dubbed Survival Pack, will offer a plethora of new content. In terms of campaigns, the game will receive two full versus mode campaign additions, a welcome change given that only two were available when the game launched. They're also introducing a new game mode called Survival, though no details were given on how this differs from the existing co-op or versus modes.
Availability and pricing information wasn't released either, though a simultaneous launch on the Xbox 360 and PC is expected. It's rumored that the update may be free at least for PC users, as it is usually the case with Valve, though we will not know for sure until it actually is available. Lastly, Valve noted that it will release the Left 4 Dead SDK this spring, enabling users to create custom campaigns and levels for the game.