Bandai Namco has detailed the online modes for SAO: Fatal Bullet:

SWORD ART ONLINE: FATAL BULLET includes eight-player competitive and four-player cooperative online multiplayer modes:

Online Battle – Up to eight players are divided into Alpha and Bravo teams and compete to cause the most damage to a boss character that populate the map. Threats come from all angles as players manage their time damaging boss character while also denying the other team from scoring points.

Online Cooperative Battle – Four players and their ArFA-sys support characters team up to take down the enemy boss.  Players must make use of their unique skills and carefully consider their roles as they complete their objective.