More than likely the title refers to events that happen in Avengers: Infinity War and if we knew the name of the next movie, we’d know what happens in that movie.
While we don’t know exactly what the story of the two Avengers films will be, the fact that the two movies were previously being called Infinity War Part 1 and Part 2 certainly led us to believe that the Infinity Gauntlet would be an important part of both stories, so naming the second film after it would not be much of a shock.
Recently, our own Eric Eisenberg got to sit down with Marvel head honcho Kevin Feige, and Feige told him that the reason the title of Avengers 4 had not been released was that it was actually a spoiler.