Left 4 Dead 2's forthcoming Cold Stream DLC expansion is open for PC and Mac beta testing now, publisher Valve has announced.
Next time you boot the game up you should notice the new addition to the campaign list. Valve wants you to take a look and then offer feedback and bug reports via the add-on's official forum. The finale in particular demands your attention as that is set to "change massively" following the beta.
First announced last month, Cold Stream started life as a community campaign created by modder Matthew Lourdelet. It caught the eye of the folks at Valve who then decided to jump in, buff it up and give it a full release.
"Matthew has been hard at work on the map and the initial release looks a little more polished than you may have expected," read a post on the Left 4 Dead Blog.
"The reason for that is the difference between how we work on a campaign compared to modders. When we work on a campaign, we normally work in a rougher state without textures for a long period. Level design artists come in later and give the game its finished look with textures.
"Modders often texture early as they have to create the structures based on the available artwork. They don't have a team of artists coming in after them. So don't let the level of texturing fool you. The campaign is still in flux."
There's no console beta planned but, as previously announced, the finished campaign will be released for Xbox 360 along with the three remaining Left 4 Dead 1 missions. No official date has been set, but it's not expected until after Portal 2 ships.