Contrary to previous titles, split-screen co-op will not be featured in Battlefield 3 which means the co-op portions of the game will be strictly online said Karl Magnus Troedsson, DICE's General Manager, at this year's Gamescom.
Troedsson did not go far into why this decision was made, however, he did say that players will "have to be online to do co-op." Troedsson also mentioned that these co-op adventures will be separate from the campaign and split into six levels. They will run anywhere from 20 to 45 minutes long depending on the level, the player's ability and the difficulty set. Players will be able to compare their scores and times from these levels with their friends and they can also earn points for teamwork during the level's duration. Troedsson also promises that some factors within these levels will be randomized giving players a new experience each time they come back.
Expect to see all this and more when Battlefield 3 hits shelves October 25th.