Avengers: Infinity War originally had a Part I and II. But now, that's been scrapped, and have but one Infinity War, while what will be the fourth Avengers movie remains unnamed. Why? Because it's planned name would be a spoiler.
Speaking to CinemaBlend, Producer, and master of Marvel Movies, Kevin Feige was asked if revealing the title of the movie would be a spoiler, to which he said, "Yeah, for sure."
When asked about the similarities between the movies and who will be returning, Feige simply said, "They're two very different movies, that's all I'll say."
This must mean something big is going to happen in Infinity War. What will it be? Avengers: Infinity War is scheduled for release May 4, 2018, with the unnamed Avengers 4 slated for May 3, 2019. We'll have to be patient for the first of the two to release first before many more assumptions can be made.