Final Fantasy XV's multiplayer DLC, Comrades, was supposed to come out on October 31 but Square Enix ended up delaying its release. It has now confirmed the expansion will become available on November 15 instead. The original release date was announced a couple months ago.
Comrades is included in the game's DLC Season Pass. If you're buying it independently, Square Enix has yet to say how much it costs.
The content in this multiplayer expansion is set after Chapter 13 of the core game. Comrades lets players complete quests with up to three other people.