Cold Stream

Cold Stream is an upcoming DLC for Left 4 Dead 2. It was announced in a blog post on February 16, 2011. It will feature Cold Stream, a community-made campaign from the creator of 2 Evil Eyes, as well as ports of additional Left 4 Dead campaigns. A release date has not yet been annouced, although it is expected to follow the release of Valve's next game Portal 2.

A beta was released on March 22, 2011 on Steam.

Beta
Cold Stream was released to the public on the official servers on PC/Mac via beta release on 22th March 2011 for playtesting and bugseeking, such as finding nav-mesh bugs, navigational issues, hit box problems, missing zombie ladders, art problems, and more.

An in-game bug reporter was activated at the same time allowing players to send feedback and bug reports. This feature was announced by Valve to be extended eventually to work with other community campaigns. But strangely, there's no "Report Bug" button in the main menu or the in-game menu, which requires writing "bug" in the Developer Console yourself.

Players can also post feedback on the official forums in the Cold Stream section. Development of Cold Stream can also be followed on Valve's official twitter account located here.