Warhammer 40,000: Space Marine is out next week. And developers Relic have only today revealed the fact the game will have a co-op mode. It's a late addition to the game; so late, in fact, it won't be available until next month.
The co-op mode, called Exterminatus, has two maps, and lets up to four players take control of a Space Marine in what's essentially a Horde match, fighting wave after wave of increasingly difficult alien enemies.
It'll be free, and will be released in "early October".