The Left 4 Dead Blog has a recent post about the release of the upcoming DLC for Left 4 Dead 2, saying that since well over 20,000 players earned the Stream Crosser achievement in the specified time-frame, they will be releasing the Dead Air DLC early, though exactly when is still up in the dead air: "We are going to try and release it as early as possible but will release it on July 22nd the latest. It isn’t currently ready for release as we have been working on The Terminal and Finale maps and need to test them more internally." Thanks VG247.