The Passing

"The Passing will become the most important campaign in the Left 4 Dead story, as all the Survivors are being called together in one campaign."

- Doug Lombardi

The Passing is an upcoming DLC for Left 4 Dead 2 which includes a new campaign and "a new co-operative challenge mode of play.". The Add-on also includes new weapons, one melee and one firearm, and a new Uncommon Infected. The new campaign takes place between Dead Center and Dark Carnival in a rural town in Georgia. It will also feature a meet up between the Left 4 Dead 2 survivors and the original survivors. The campaign will be playable in all the game modes including the new game mode. Valve hasn't announced pricing details yet, but they do have a target release window: "early spring" for both the PC and Xbox 360 versions.

An interesting note, the voice clips for the Left 4 Dead 2 Survivors informally introducing themselves are already present in the game files.