The previously rumoured Assassin's Creed III co-op multiplayer mode is indeed real.
It's called Wolf Pack and supports up to four players as they attempt to track down and assassinate NPCs throughout 25 sequences, in what sounds like a spin on the standard Assassin's Creed multiplayer. Wolf Pack was revealed at Comic Con and picked up by IGN.
Assassin's Creed III launches at the end of October for PS3 and 360, and on Wii U around the console's launch. A PC version will be out before Christmas.