https://www.cnet.com/news/fallout-76-might-be-an-online-survival-rpg-like-dayz-or-rust/

The trailer was predictable, maybe even obvious -- but according to a report from Kotaku, the game itself might not be what you expect of a Fallout game. Sources told Kotaku that Fallout 76 started life as a multiplayer prototype for Fallout 4, but slowly evolved into an online survival RPG that takes inspiration from games such as Rust and DayZ. 

The sources say the game will still have quests and a main story, just like traditional Fallout games, but will also have a focus on base building and online multiplayer. On Twitter, Kotaku's Jason Schreier elaborated, explaining that from what he's heard the game isn't necessarily an MMO, but it's "not strictly single-player."