Valve's quest to inject original Left 4 Dead episodes into Left 4 Dead 2 continues. Today's Left 4 Dead 2 update includes the new version of the Terminal Map for Dead Air, the game's official blog revealed.

To entice people to test the update, the team at Valve is offering players a prize: the beta version of the Blood Harvest campaign for Left 4 Dead 2. Getting the prize won't be easy, however, as players will have to accomplish a difficult task together.

A new achievement, dubbed "Connecting Flights," has been added to Left 4 Dead 2, which unlocks when players play "a complete game of Versus in Dead Air." When 60,000 people have earned the achievement, Valve will unlock the beta version of Blood Harvest on Steam "the next weekday."

Previously, Valve offered to unlock Dead Air early, if 20,000 L4D2 players unlocked a freshly created achievement. A mere 24 hours later, the goal was shattered.

This time, Valve is making it harder to accomplish the goal. "60,000 is going to be hard," the official blog noted. "You can’t rage quit and you need to work together. Once you get the achievement, help others get it as well."