Fallout 76 was briefly shown off at Microsoft's E3 2018 presentation. This was just hours of ahead of Bethesda's own E3 2018 show, later that same day.
Todd Howard appeared on Microsoft's stage to firstly reveal that Fallout 4 was available on Xbox Game Pass right now. He then moved on to detailing the upcoming Fallout 76.
The Bethesda director revealed that Fallout 76 is four times the size of Fallout 4, and that it's set in the hills of West Virginia.
This was all the information we had on Fallout 76 in the Microsoft presentation, and we'll have to wait until later in the Bethesda presentation for more.