https://www.pcgamer.com/the-enclave-are-one-of-fallout-76s-factions-bethesda-confirms/

Perennial Fallout baddies The Enclave—who featured heavily in both Fallout 2 and 3—will return as one of the factions in Fallout 76, Bethesda has confirmed.

The developer tweeted the below image, giving some backstory for the faction and revealing that they have a "secret bunker" hidden somewhere in Appalachia, where the game is set.