Marvel has been building to The Avengers: Infinity War - Part I and Part II since we caught that glimpse of the Infinity Gauntlet in Odin's trophy room in Thor. But according to directors Joe and Anthony Russo, the titling of the big finale is still in flux.
Talking to Uproxx, Joe Russo said:
“The intention is we will change it, we just haven’t come up with the titles yet. But, yes, we will change it. And, yes, that is a scoop: we will retitle them.”
The reasoning, according to Joe Russo, is because the films are "two very different movies" and that labeling them Part I and Part II is misleading for audiences, perhaps suggesting they are only getting half a movie, à la Harry Potter and the Deathly Hallows or Mockingjay.
We know that the Marvel Cinematic Universe is all connected to one larger story anyway, so it makes sense to keep the movies as separate entities without running the risk of alienating folks, who might have skipped Part I, from seeing Part II.
But who am I kidding? We're all going to see these movies no matter what they're called.