Officially, Marvel has been careful not to reveal any Avengers 4 story details, though there’s been plenty of unofficial chatter and speculation, from the movie picking up years after Infinity War to the surviving heroes venturing into the Quantum Realm.
For years we had no idea what to expect from Avengers 4, but when Thanos snapped his Infinity Stones-powered fingers and wiped out half of all life in the universe at the end of Avengers: Infinity War, that set the stage for what will be the final Phase 3 movie.