https://www.gamespot.com/articles/e3-2018-bethesda-confirms-fallout-76-is-an-always-/1100-6459647/

We have finally learned exactly what Fallout 76 is. At the Bethesda E3 2018 briefing, director Todd Howard confirmed that Fallout 76 is a multiplayer-focused, always-online game. The characters you come across in Fallout 76 are real people. The game is entirely online, marking a dramatic shift away from the single-player-only nature of earlier games in the series.

However, you can also play by yourself, Howard confirmed. "Of course you can play this solo," he said. Regarding why Bethesda is taking Fallout in such a new and different direction, Howard said, "We've always wanted to see what our style of game could be with multiplayer."