Russo brothers confirm AVENGERS: INFINITY WAR sequels will have different titles.
Several months ago, directors Anthony and Joe Russo stated that the two-part sequel known as a whole as Avengers: Infinity War will have two different titles. Avengers: Infinity War – Part I and Avengers: Infinity War – Part II are “two very different movies. It’s misleading.”
At the time, the Russo brothers confirmed that there would be different titles for the sequels, with no indication as to what they would be called. But recently, Disney announced that the title for The Avengers sequel being released in 2018 is simply Avengers: Infinity War. The new title implies what fans think will happen; they believe Thanos will get both the Infinity Stones and the Infinity Gauntlet by the end of the first movie.
As for the sequel, it still has the moniker of Untitled Avengers. It is clear that the Russo brothers want to keep the two movies very distinct from one another. We don’t know much about The Avengers: Infinity War. But the basic plot points stem from the Infinity Gauntlet and Infinity War storylines of Jim Starlin‘s comics.
The Avengers: Infinity War is expected to be released May 4, 2018. Untitled Avengers has a tentative release of May 3, 2019.
(Source)