Duke Nukem Forever - Free Multiplayer Add-on pack announced

Here are the contents of an e-mail sent to all member's of the "first access club":

"Hello First Access Member,
As the launch date for Duke Nukem Forever approaches, we would like to offer a heartfelt thanks to you, the true believers who have already placed your bet on Duke with your pre-order, or Borderlands Game of the Year purchase. As a sign of our appreciation, Gearbox Software and 2K Games are thrilled to present every First Access Club member who has registered as of today the very first Duke Nukem Forever multiplayer downloadable add-on for free!* Surprise! Thank you again for all of your support. We're almost there.
Hail to the King, Baby!
Gearbox Software and 2K Games"


I wonder what is included in this pack?