Faliszek also noted that the content will be free -- like usual -- for Steam users, and the series will be arriving on Steam for Mac as well. If that wasn't enough, L4D1's "No Mercy" campaign has been updated for the sequel and will be included with "The Sacrifice" when it ships. Though players will be able to choose which crew member passes in "The Sacrifice," a 150-page, four part digital comic details events leading up to the new DLC will have a more definitive finale which will effect the future content for the series (we can't be more specific without spoiling "The Passing"). Faliszek didn't give a price or a release window on the show, but he did admit that this "is not the end, we're gonna continue going" with future content for the series.
Update: According to an interview with PC Gamer (via Shacknews), it seems "The Sacrifice" will be available (at least on PC) as of October 5 for free, though it will cost 560 MS Points ($7) on Xbox 360. We've reached out to Valve for clarification on the release date for 360 and Mac.