https://www.gamespot.com/articles/how-sea-of-thieves-progression-system-makes-sure-y/1100-6455647/

Although Sea of Thieves can be played solo, cooperative multiplayer is a major component. Oftentimes, friends can have trouble playing co-op games together if they haven't invested the same amount of time in them, but with Sea of Thieves, developer Rare has its sights set on a progression system that works differently.

Sea of Thieves' release date was recently announced for both Xbox One and PC: After a number of delays, it's due out on March 20, 2018. The game features cross-play, allowing players on both platforms to take to the high seas together.