Space Marine co-op will be added to the game free of charge in early October, developer Relic has announced.
It will be four-player online co-op free to anyone who buys the game.
The mode, called Exterminatus, is Space Marine versus Orks and the Forces of Chaos.
All three multiplayer classes: Tactical Marine, Devastator and Assault, are available. Perks unlocked in the competitive multiplayer mode can be used, and co-op progression will apply to your multiplayer ranking, meaning you can unlock perks and weapons through it.
Exterminatus will initially launch with two scenarios: Assault on Hab Center Andreas and Escape from Kalkys Facility. Each will include multiple arenas. Co-op is score based, with global leaderboards. Multipliers and dynamic challenges will help teams boost their scores.
The game itself launches next Friday in the UK.