Although it was supposed to be available by the end of the month, Deep Silver and Techland have announced that there will be a delay in the release of the Bloodbath Arena DLC pack.
"We are working hard to make the Bloodbath Arena DLC available as soon as possible. However, due to further polishing of the main game the finalisation of the DLC code has been delayed. We know that many fans are eagerly waiting for it and apologise for any inconvenience. We expect to announce a release update next week."
Bloodbath Arena will be available free to those who purchased the special edition copy of the game and is expected to cost $10 for everyone else. The DLC pack includes a new weapon, separate leaderboards, and 4 arenas where you'll fight waves of zombie attacks:
"...the Bloodbath Arena pack features single and multiplayer challenges in four different arenas. It’s a pure fight for survival when wave after wave of deadly zombie attacks, one more gruesome than the next! Characters can also gain additional experience points and items and bring them over to their single or multiplayer campaigns. What’s more, players can show off their skills in zombie fighting via the Bloodbath Arena’s Leaderboards. Finally, Bloodbath Arena includes a new exclusive weapon, the brain wave bomb, to ensure some highly explosive combat experiences."