[UPDATE: James Gunn has shed some light on this matter.]
With just a little less than a year to go until its release, Avengers: Infinity War is starting to look less and less like the faraway possibility it once was, and more like an impending reality fans can start preparing themselves for. But just because the studio is in the very middle of the intense production schedule for Infinity War, doesn't mean that Kevin Feige and everyone involved in the film aren't still being constantly asked about the very mysterious Avengers 4. Originally titled Avengers: Infinity War - Part 2, the film has been covered in a shroud of mystery over the past year or so, when Marvel changed the film's title and the production schedule that originally connected it directly with Infinity War.
Following the announcement of Josh Brolin being cast as Cable in Deadpool 2, many fans have started to wonder if the two-part event films would actually be continuations of the same story, featuring the same characters and villains, or if they may be different, still only somewhat connected films thematically. Even recently, Kevin Feige came out and said that the title for the film would spoil Avengers: Infinity War, hence why the studio has yet to announce what it is.
As a result, the Marvel fandom has been busy speculating as to what may or may not happen at the end of Infinity War that leads into Avengers 4, and specifically how the conflict with the Mad Titan may or may not carry over. But in a recent interview with the BBC's Lizo Mzimba, Gamora herself, Guardians of the Galaxy Vol. 2's Zoe Saldana may have revealed the title of the fourth Avengers film to be Avengers: Infinity Gauntlet:
— lizo mzimba (@lizo_mzimba) April 24, 2017
For some fans, this news may be a bit confusing, since the Infinity Gauntlet title may not be considered much of a spoiler amongst the more diehard Marvel fans and comic book readers. But this title does imply something interesting, which is that the two films may be divided entirely around Thanos' quest to assemble all of the Infinity Stones into the Infinity Gauntlet. What this title suggests is that Avengers: Infinity War may be entirely about Thanos acquiring all of the infinity stones for himself in order to complete the glove, and the MCU's heroes fighting to make sure he doesn't, which some fans may not have been expecting.
So if Saldana's comments here are indeed indicative of what The Avengers 4's title is, then Infinity Gauntlet means that Infinity War likely ends with Thanos successfully assembling the glove, while Infinity Gauntlet focuses entirely on him abusing the power, and the heroes then having to try and stop him before he literally wipes out all life in the galaxy. Now, make sure to take this all with a grain of salt for the time being, since neither Kevin Feige nor anyone at Marvel have confirmed Avengers: Infinity Gauntlet as the film's title. But it would certainly make sense if the films are still very much two halves of the same whole, and promises that the two films may offer a much more well-paced and patient retelling of the Infinity War and Infinity Gauntlet's story, rather than if they had been completely compressed into just one film.
UPDATE: James Gunn has addressed this matter at the Guardians of the Galaxy Vol. 2 press junket in Europe, telling Yahoo! Movies point-blank that Infinity Gauntlet is not the title of the fourth Avengers movie:
“My guess is that Zoe just misspoke. I’ll talk to Zoe today, but I would imagine that is just Zoe misspeaking and saying ‘Infinity Gauntlet’ instead of ‘Infinity War’.”
Source: Lizo Mzimba
Update Source: Yahoo! Movies