Valve is planning on releasing the classic Left 4 Dead 1 episode ‘Dead Air’ early as a thank you for helping them beta test the new community created map ‘Cold Stream’. Valve challenged the community to unlock the “Stream Crosser” achievement 200,00 times by completing the episode. Within four and a half hours the community had reached their goal and after 24 hours Valve reported that the achievement had been unlocked 60,774 times.
Due to the success of Cold Stream, Valve has promised to release the long awaited Dead Air campaign on PC and Mac as early as possible but by July 22nd at the latest. Additionally Valve mentioned they have been busy testing a new finale for the L4D2 Dark Carnival and gameplay improvements to some the rest of the episodes’ finales. Valve said that Cold Stream and the L4D episodes will be released on Xbox 360 once they have been thoroughly tested on PC.
Source: L4D Blog