Several months before Joss Whedon’s Avengers: Age of Ultron released, Marvel Studios announced plans to deliver Avengers: Infinity War – Part 1 in May 2018 with Avengers: Infinity War – Part 2 arriving in theaters the following summer.
Avengers 3 stayed as Avengers: Infinity War (without the “Part 1” portion, of course) and Avengers 4 remained untitled for the time being.
Speaking with Screen Rant’s Rob Keyes and other a handful journalists and bloggers on the set of Avengers: Infinity War last summer, Joe Russo briefly discussed their approach to filming both Avengers movies back-to-back despite the movies technically being separate films.
Avengers 4 is in a peculiar situation of being a direct continuation to this summer’s Avengers: Infinity War while also having a unique story.