At a press conference in Amsterdam, Bungie confirmed that Halo 3 will feature an online cooperative mode for two to four players. Further details are unclear: does this mean you can play through the single-player campaign as a team of four, or is it a discrete game mode? Is there drop-in, drop-out? Etc.
Bungie's Luke Smith confirmed the news (originally reported in a language that is not English) on NeoGAF, and said details will hit Bungie's official site later today.
[via Joystiq]