Just when you thought the zombie apocolypse couldn't get any more horrifying! Valve recently announced its plan for Left 4 Dead DLC, and we've got the first look. Valve is opening up Death Toll and Dead Air for versus campaigns, and even more exciting is a new multiplayer mode called Survival, where up to 4 players set records for the longest time surviving hordes of Zombies on over 12 maps. This new mode will be available for download or as part of a special edition for Left 4 Dead coming this Spring.
So, it looks like the 'new' versus campaigns will indeed be Death Toll and Dead Air, as expected, and the survival mode is presumably a kind of stronghold mode, where your aim is solely staying alive rather than the progression through the level.
The "over 12 maps" to be available for Survival mode is most likely the maps already in the game that are best suited to the new mode, and not new arrivals from Valve. As a result it looks like the update won't have any new content on that front.
You can find the information in this video, at 18:43. There is no footage of the new mode as of yet.

















