Valve's announced an October 5 release for The Sacrifice, the new story DLC for both Left 4 Dead 1 and Left 4 Dead 2 on 360 and PC.
The Sacrifice is a prequel to what happens in Left 4 Dead 2 DLC, The Passing, and lets you play through it as the survivors of Left 4 Dead 1.
As well as more story, the content introduces "a new style finale" known as "Sacrificial Gameplay," where you get to decide who dies and who lives on to fight another horde.
As well as The Sacrifice, anyone who downloads it for Left 4 Dead 2 gets L4D1 campaign "No Mercy" for L4D2.
Valve has confirmed that both campaigns will be playable in "Versus, Survival, and Scavenge modes," as well as Campaign.
It'll also feature "the Left 4 Dead 2 Special Infected, items, and weapons."
The Sacrifice will cost 560 MSP for those buying on 360, but will be free to get on PC.