It looks like Sunset Overdrive has 8-player co-op

Sunset Overdrive appears to have co-op play for up to eight people, according to a since-pulled listing on the Xbox One…

Sunset Overdrive will have eight-player co-op - Gematsu

Sunset Overdrive, PC Steam Game

Join the 'Chaos Squad' in Sunset Overdrive's multiplayer trailer

Chaos Squad, Sunset Overdrive Wiki

Sunset Overdrive video details Chaos Squad multiplayer mode - Gematsu

Sunset Overdrive Dev Wants to Bring Game to PC, But Microsoft Gets to Make the Call : r/pcgaming

Rumor: Sunset Overdrive will feature 8-player co-op multiplayer

An Open World with No Rules: Leap off buildings, run along walls, and grind power lines and rails to destroy your foes from every angle. Lethal

Sunset Overdrive Day One Edition - Xbox One

Sunset Overdrive's getting crazy with eight-player co-op – Destructoid

An Open World with No Rules: Leap off buildings, run along walls, and grind power lines and rails to destroy your foes from every angle. Lethal

Sunset Overdrive Day One Edition - Xbox One