UPDATE: James Gunn has told Yahoo Movies that Avengers 4 is not titled Avengers: Infinity Gauntlet. He thinks that Zoe Saldana simply misspoke. He says, “It's not the title. 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'.”
In their October 2014 Marvel Cinematic Universe Phase Three announcement, Marvel Studios followed a Hollywood trend by revealing that the third and fourth Avengers movies would actually be a two-part sequel titled Avengers: Infinity War Part 1 and Part 2. But in July 2016, they back-pedaled, updating the third movie's title to Avengers: Infinity War, and discarding the title of the fourth altogether. The Russo Brothers explained that the changes were made to clarify that the two movies would be "very different and distinctive".
Just a couple of days ago, Marvel President Kevin Feige suggested that the Avengers 4 title would be kept under wraps for a while, because revealing it would spoil the ending of its forerunner. But did Zoe Saldana, who portrays Guardians of the Galaxy member Gamora in the MCU, let the mysterious title slip during the Guardians of the Galaxy Vol. 2 European Gala event? When English journalist Lizo Mzimba asked her about Avengers: Infinity War at the event, the 38-year-old actress responded:
We’re in the middle of it. I think that the Guardians just shot their part when it comes to Infinity War, it’s like the first part, and we all have to go back for Gauntlet later this year.
"” lizo mzimba (@lizo_mzimba) April 24, 2017
The interviewer is confident that Saldana’s “Gauntlet” comment indicates that the title of the fourth Avengers movie is Avengers: Infinity Gauntlet. To be honest, it’s neither a SPOILER-ish nor a surprising title, since a number of people predicted it when they learned that the two movies would no longer have the Part 1 and Part 2 titles.
Of course, it's also entirely possible that Gauntlet isn’t the Avengers 4 title at all. Maybe Infinity Gauntlet is just a working title used among the cast members. But if that isn't the case, Feige must be a bit irritated with Zoe Saldana right now!