The Space Marine community has been waiting for the "Exterminatus" add-on for some time, and yesterday, THQ released the new mode to Steam and PSN as a free download. Xbox LIVE members, however, noticed that they never got the supposed update to download and install the new co-op mode.
What gives? Turns out, THQ and Relic are having some issues with the Xbox 360 version, and after a day of waiting, THQ Community Manager THQSledgehammer (or Sledgehammer70) posted an update on the official forums explaining the problem:
"Prior to the release of the Xbox 360 version of the Exterminatus DLC it came to our attention that there was a connectivity issue that needed to be fixed. We have taken the difficult decision to delay the title update and DLC release to repair this issue and ensure that the mode is functioning as intended when we release it. We will share a projected live date for this content on the Space Marine community site as soon as possible."