When the movie was first announced at a Marvel press event in October 2014, which laid out the entire Marvel Phase 3 slate, it was revealed that the third and fourth Avengers movies will be Avengers: Infinity War – Part 1 and Avengers: Infinity War – Part 2, but that was later changed, with the first movie now titled Avengers: Infinity War and the Avengers 4 title yet to be revealed.
During an interview on the set of Avengers: Infinity War, The Russos revealed why the project shifted from a two-part story to being two completely separate movies.
Many are still wondering what the official title for Avengers 4 will be, and since it has been confirmed that the Avengers 4 title is in fact a huge spoiler for Avengers: Infinity War, it’s possible that the Avengers 4 title will be revealed during the end credits of Avengers: Infinity War.
Joe Russo also compared Avengers: Infinity War and Avengers 4 to the two movies that started the trend of splitting the final movie in half, Harry Potter and the Deathly Hallows.