
Marvel Studios has already revealed some major details about its upcoming X-Men film, which will be a part of Phase 7 of the franchise following Avengers: Secret Wars. Many fans have been begging Marvel Studios to develop an X-Men movie set within the MCU for some time now. Characters from Fox's X-Men films will be featured in Avengers: Doomsday and Avengers: Secret Wars, but after those movies and the Multiverse Saga, an entirely new group of familiar Mutants will be introduced in the MCU.
The Script is in the Works

Marvel Studios has not begun rolling the cameras on its upcoming X-Men movie yet since all eyes are currently on the upcoming Avengers movies and Spider-Man: Brand New Day. However, the script is currently being written by Michael Lesslie. Notably, the movie has also found its director, Jake Schreier, who seemingly has a lot of input on the script as well.
Marvel Studios President Kevin Feige revealed in July that the script was "underway." There is no way to tell exactly how long it will take to write, but since X-Men won't be a part of the MCU until Phase 7, Lesslie and Schreier have some time to make sure it is exactly how they want it:
"It’s official, Jake Schreier is doing 'X-Men' for us, and we're very, very lucky. And we're very, very lucky to have him and very excited to have him. And so we're beginning. It's all starting now. The script's underway."
Jake Schreier is Directing

As mentioned, Marvel Studios already announced that the studio brought Jake Schreier back to direct X-Men. Schreier previously sat in the director's chair for Thunderbolts*, an MCU film that received a lot of critical and fan praise, but didn't perform well at the box office.
Marvel Studios apparently liked what it saw from Schreier with Thunderbolts*, though, as the X-Men movie will definitely be an entry that the company will want done right.
Schreier recently confirmed that he had begun working on the project, meaning that he is definitely involved with the writing process and pre-production. He also revealed some storytelling elements that will be in the film:
"I can’t say anything about it, but we’ve started work on 'X-Men,' and that’s obviously very, very exciting."
Specifically, the director teased that X-Men will feature some highly emotional moments while also showcasing patented MCU action. Fans who watched Thunderbolts* will be familiar with Schreier's ability to balance the heartfelt moments with the explosions, and it sounds like he will be bringing more of that to X-Men:
"There are so many things that I didn’t know about before I started '[Thunderbolts*].' The biggest learning curve for me was the proportion of the action to the more emotional, character-driven scenes, and how, even though it’s more shooting days than I’ve ever had, they get eaten up quite quickly by the action stuff. By the time we got to the end of it, it felt like, 'Oh, now I feel like we get how to do this a little bit better.'"
A Youth-Oriented Cast

One major detail Marvel Studios has revealed about the upcoming X-Men film is that it will feature a younger cast, potentially meaning that the same actors and characters could be showcased within the MCU for many years to come.
Feige also revealed that the script and the film will be targeting a younger demographic, specifically saying that it "will be a very youth-oriented, focused, and cast movie:"
"Jake's an incredibly smart guy, and he's an incredibly talented filmmaker. We had a great experience with him on 'Thunderbolts*.' And if you saw that movie, what he did with those character interactions, he also has his pulse on, shall we say, a younger demographic. He’s younger than me for sure, but he's tapped into that in a way that I think was important for 'Thunderbolts*,' much more important for 'X-Men.' Because 'X-Men,' as it was in the comics, will be a very youth-oriented, focused and cast movie."
Since the movie is still very early on in development, no casting announcements have been made yet, and likely won't be for some time. However, that doesn't mean there aren't some specific actors Marvel is already eyeing.
It is also worth noting that more than a few actors have been the subject of casting rumors for X-Men. Whether those come true or not will remain to be seen, but it is always possible that at least a few of the rumored names will make it into the film.
It Will Be Visually Different Than Previous X-Men Films

The X-Men have always been extremely popular heroes, and the style of how they have been portrayed on-screen throughout the years has been rather unique. However, the movie that will be coming in Phase 7 will be "recognizably different from what came before," at least according to Jake Schreier.
In a press conference prior to the release of The Fantastic Four: First Steps that was shared by Variety, Schreier admitted that the MCU's version of X-Men will be different from anything fans have seen before regarding the group of Mutants:
"Yeah, I think that’s fair to say ['X-Men' will be] recognizably different from what came before."
As Marvel Studios has done with some of its more recent movies (like The Fantastic Four), Schreier also revealed in that same interview that X-Men will draw a lot of inspiration from the comic books, particularly when it comes to "scale:"
"But to be able to explore all of the ideas that are inherent to that rich source material, but also at the scale inherent to the source material, that’s like a very rare and fortunate opportunity. That’s very exciting."
Will Build Towards a Saga Adapted from the Comics

One of the biggest details that has come straight from the mouth of Kevin Feige regarding X-Men is that it will be adapting some kind of saga from the comics. It is unclear what saga this will be, but it will likely culminate with an Avengers-level film solely centered around the X-Men.
Specifically, Feige talked about how the first film will be "introducing all of [the] characters and giving them their due," while also setting up that major saga.
The Marvel Studios boss also mentioned how the X-Men have a "comic legacy" just by themselves, implying that it is important to Marvel Studios to give them a bit of freedom from the greater MCU while also making sure they are still tied in:
"So a lot has been done. But again, because it's X-Men, because it's almost a comic legacy unto itself, there’s so much more to tap into it. And there [are] so many sagas within sagas for X-Men that that’s part of what we’re talking about now — which saga to grow and build to while doing the most important thing, which is introducing all of these characters and giving them their due in our first film."
Its Plot Will Be Impacted by Secret Wars

Avengers: Secret Wars is expected to be the biggest Marvel movie to ever be released, so it will be no surprise to many to hear that X-Men will be directly impacted by what goes on in that film.
However, that is not just a prediction. Kevin Feige recently talked about how Marvel Studios is already planning out and developing Phases 8 and 9 alongside Phase 7.
The boss also specifically made it a point to say that the first phase of the next saga, which would be Phase 7, will be "directly impacted" by what goes on in Secret Wars, and even Doomsday:
"A saga is three phases, so we’re working on the next three right now. But really, the first one of the next saga is directly impacted by what we’re doing right now with these movies and 'Secret Wars.'"
It has not been confirmed that X-Men will be a part of Phase 7 yet, but that seems like the most likely destination for it. An Avengers movie likely won't be released during Phase 7, so it needs some kind of major title to represent it, and X-Men makes the most sense.
X-Men Won't Release Until 2028 at the Earliest

As mentioned in the previous section, Marvel Studios is already intricately planning its future, which includes filling release dates for feature films.
Avengers: Secret Wars will not be coming until 2027, a year that will see the release of three total Marvel Studios titles. X-Men is not far enough into development to be released in 2027 since it will likely be such a big movie, but even if it were, Marvel would probably want to hold off on releasing it so that two major films aren't in the same calendar year.
It is also worth noting that Marvel has reportedly filled all of its 2027 release slots, with none of the titles being X-Men. Therefore, the Mutant movie will not see the light of day until 2028 at the earliest. It is possible that it could even be pushed back until 2029, but fans will likely know more once the Multiverse Saga is over.