The downloadable add-on will be available to owners of the PC version at no cost, with Xbox 360 players needing to pony up 560 Microsoft Points ($7) for the experience.
"New locations, new dialogue from the original cast, and an explosive finale" were promised, with Valve noting that the download--meant to bridge the gap between the existing "No Mercy" and "Death Toll" campaigns--will also bring new Survival maps alongside the new single and multiplayer campaign.
"The primary goal of 'Crash' is to deliver a complete Versus mode experience in just 30 minutes, resulting in a streamlined version of the game's existing Versus campaigns," the company explained. "A recharge timer for infected teammates has also been added, and item spawn behavior has changed for more balanced gameplay."
"We're working with the fans toward the ongoing entertainment value of the product," said Valve founder Gabe Newell.
Though the controversial sequel to Left 4 Dead, appropriately titled Left 4 Dead 2, is due to hit PC and Xbox 360 on November 17, the studio has previously pledged that it will "keep supporting Left 4 Dead 1" and hopes that once "everyone's had time to see the complete product of Left 4 Dead 2 and see continued support for Left 4 Dead 1, they may sort of see what we were up to and what the method of our madness was."