After a short Baldur's Gate 3 demo we sat down with Larian's founder Swen Vincke to talk about the early access plans as well as the huge scope of the game.
Currently the first act of the game that is realising with the early access version is bigger than the entirety of Divinity: Original Sin 2, with more to be added to the locations, classes, spells and races as development on BG3 continues.
While multiplayer will be in the game when Baldur's Gate 3 (maybe) releases in early access in August 2020, there is not currently a Dungeon Master mode in development.