Valve has announced a series of content and development releases for its latest title Left 4 Dead.

The first L4D DLC - dubbed the L4D Survival Pack - is due for release this autumn and introduces a new multiplayer game mode entitled "Survival" plus two complete campaigns for Versus Mode. A Critic's Choice Edition of the game is also heading to retail stores at the same time, and will include access to all the content introduced in the L4D: Survival Pack.

In addition, for PC gamers and aspiring developers, the first Left 4 Dead release for the Source Software Development Kit (Source SDK) will allow the creation of custom Left 4 Dead campaigns that will be discoverable via L4D's matchmaking system. The SDK update is also due for release this spring, and is free of charge to all owners of L4D on the PC.

"Since Half-Life launched in 1998, Valve has made continuous efforts to expand the offering of its products beyond what's included on the day of launch," said Gabe Newell, co-founder and president of Valve. "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. 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."

For more information, visit the official site.