To us, it sounds more like Bethesda is opting for a really brief early access period as opposed to a traditional beta.
The upcoming Fallout 76 B.E.T.A. (Break it Early Test Application) won't simply be a vertical slice of the game. "We hope you join us!" The game's pre-order page also allows you to select Best Buy, Amazon, GameStop and Walmart as your retailer if you're in the USA and playing on PC; different retailers are listed based on location and platform. If you pre-ordered through a retailer, you'll need to head to Bethesda.net, create an account, and redeem your code - this will either be on your pre-order receipt or email confirmation.
Quake Champions, Fallout Shelter both started out as Bethesda launcher-exclusive games before later coming to Steam.
It's easy to end up logging a couple of hundred hours ina Fallout game, so the bonus of all progress made in the B.E.T.A being carried over to your game when it releases will mean players can jump in exactly where they left off.
One of the examples given is that if your base gets blown to smithereens by a nefarious group of wasteland wanderers, expect the radiation to be still giving you sickness when you play upon launch.
Fallout 76 is set to launch on November 14, 2018 for Xbox One, PlayStation 4, and PC.