Valve’s announced that upcoming community-made L4D2 DLC Dead Air will launch on the week of July 22 at the latest. It has said it’ll try to release it earlier than that, but July 22 is the latest date it will release on. The early release follows a challenge for 20,000 Steam users to unlock the Stream Crosser achievement on Cold Stream. The barrier was massive surpassed at 60,774 times.
There’s more details here.