Last month, Valve announced that a new downloadable content pack was in the works that would port the three remaining campaigns from Left 4 Dead into the sequel, in addition to a new community-made campaign called 'Cold Stream.'
An announcement on the official Left 4 Dead blog today reveals that a beta for 'Cold Stream' has been released for the PC version of Left 4 Dead 2, via Steam. Those who like to hunt bugs along with their zombies are encouraged to dive in and give feedback to the developers via the Cold Stream forum.
"If you see a bug report it," states the announcement. "There are sure to be nav-mesh bugs, navigational issues, hit box problems, missing zombie ladders, art problems, etc. Remember it's a beta."
The Cold Stream beta is only available for Mac and PC players, though Cold Stream will be included in the DLC pack for Xbox 360, once it's released.