Valve has released details of the first downloadable content pack for its co-op zombie shooter Left 4 Dead - the L4D Survival Pack.
The release will include a new multiplayer mode called Survival and two complete campaigns for the game's versus mode, and be available for both the PC and Xbox 360 versions.
Also in the spring, PC users will get a free-to-download Software Development Kit allowing the mod community to start creating custom campaigns for the game - which, when completed, can be fully integrated with Left 4 Dead's matchmaking system.
All of this will be bundled into a Critic's Choice Edition of the game that will be commercially released at the same time.
No exact release date or pricing details were confirmed, and the nature of Survival mode remains a mystery for now.
"With Half-Life and Counter-Strike, and more recently Team Fortress 2, we've learned that we're no longer making stand-alone games but creating entertainment services," said Valve boss Gabe Newell, warming to one of his favourite themes.
"With Left 4 Dead we're extending that tradition by creating additional gameplay and releasing our internal tools to aspiring developers so they may also create and distribute new Left 4 Dead experiences."