Solo, but still online. Prepare to get nuked every time you're logged in for more than an hour.
Can't wait to see more info regarding the MP aspect. Is it going to be a rust style survival where you can mini nuke bases etc on PvP servers or have the option to play on a PvE style server.
According to the interview below, it seems to be more PvP only on the servers. There will eventually be mod and private server support, but not until next year likely (if the Fallout 4 Creation Kit launching several months after is anything to go by). Also no NPCs as all other characters will be other players, which seems weird because shopkeepers and such? Unless those are all robot-only. Ton more in the interview too. Just under 14 minutes long.