https://www.gamespot.com/articles/fallout-76-beta-launches-on-xbox-one-first-followe/1100-6459894/

Although the exact launch date of the Fallout 76 beta is still a mystery, we now know it will be coming to Xbox One first. On the Fallout FAQ page, the launch date for 76's beta is listed as unknown. Players are asked to stay tuned to Fallout's social accounts before being left with one final note: "the B.E.T.A. for Xbox One will begin first, followed by other platforms." Fallout 76 is scheduled to release November 14.

The beta is still scheduled to release on both PS4 and PC, but players on those two platforms will have to wait a little bit longer to play the game. Bethesda has supplied no clues as to how much earlier Xbox One players will get the beta, nor whether the Xbox One beta will end early or go on for as long as the betas on PS4 and PC.