A few important details in case you passed out from excitement:

Xbox One Beta Date: 10/23/2018
PS4 & PC Beta Date: 10/30/2018

Why does Xbox get it one week early? They didn’t say, nor are obligated to reveal why. My educated guess is that Microsoft paid the publisher money to get the preferential timing to encourage Xbox sales. This is not anything new, as there have been console exclusive games for the longest time, so having special times for a Beta test is nothing different.

Primary Goal: stress test and break the game.
What that means to you: the servers will not be running 24/7, only during “targeted timeframes” which means you shouldn’t schedule time off work to participate in the Beta. The targeted timeframes ‘might’ be anywhere “between 4 – 8 hours.”

There will not be an NDA (non-disclosure agreement) for the Beta. Players are encouraged to stream and talk about the game as much as they like.

Bethesda intends on having your progress from the Beta carry forward towards actual launch.

The download size is expected to be approximately 45GB and will not be available for pre-load.

For PC players, there are still no current minimum specs for Fallout 76 yet.

Go here for the actual FAQ.