While Sea of Thieves does feature multiplayer, SoT does not support split screen multiplayer. This goes for both the PC and Xbox versions of the game. You can only join a group of friends through online co op multiplayer.
Sea of Thieves is available as a standalone purchase for $39.99 on PC, Xbox One, Xbox Series X|S. It is also available as part of Game Pass for both PC and console.
Considering the game is a Microsoft Game Studios exclusive (developed by subsidiary Rare), SoT features cross play between PC and console, so it doesn’t matter where you or your friends own it. You can play together.
Just as Sea of Thieves will likely never come to PS4 or PS5, it’s unlikely that Rare will patch in split screen multiplayer. Since SoT is a shared, online world, playing split screen multiplayer just isn’t part of the game’s DNA, and it would take considerable work (at the minimum) to implement it.
It’s not impossible that Sea of Thieves could one day have split screen multiplayer, but the possibility of that is very small.
