
Although it is more than a few years away, Marvel Studios recently confirmed that Phase 9 of the MCU is already in development and being worked on. Phase 6 of the interconnected franchise is just beginning. The Fantastic Four: First Steps is serving as Phase 6's first official entry. Phase 6 will come to a close with the release of Avengers: Secret Wars on December 17, 2027, which will also mark the end of the Multiverse Saga, allowing Marvel Studios to begin with a fresh saga in Phase 7.
Phase 9 of the MCU is already in development at Marvel Studios and is something that has been planned out in depth, but also will continue to be planned out across the next few years.

In a roundtable Q&A with Marvel Studios President Kevin Feige that took place in California ahead of the release of The Fantastic Four: First Steps, the Marvel chief was asked about the future of the franchise, and he gave the shocking revelation that Phase 9 is already in development.
According to Feige, Marvel Studios is already "working on the next three (phases) right now," meaning that the entirety of the next saga (which is expected to be the Mutant Saga) is being worked on simultaneously:
"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.'"
Since Phase 6 is ending the Multiverse Saga, Phase 7 will begin the next saga (once again, which is expected to be the Mutant Saga). Since Feige stated that Marvel Studios is working on the next three phases and the entirety of the next saga, that means Phases 7, 8, and 9 are all in active development.
Obviously, Phase 7 is further along in the development process than Phases 8 and 9 are, but it does seem as though Marvel Studios has somewhat of a detailed plan of what Phase 9 will include.
What Films Could Be in the MCU's Phase 9?
X-Men 3

An X-Men film was confirmed to be in development at Marvel Studios. Feige also confirmed that it would be directed by Thunderbolts* filmmaker Jake Schreier, and it is expected to be released at some point in Phase 7.
Since the next saga will center around Mutants, it would only make sense for the X-Men to be the focal point of the saga. If that is the case, one would assume that an X-Men movie will be released in every Phase of the next saga.
So, it would only make sense for X-Men to be a part of Phase 7, X-Men 2 to be included in Phase 8, and then X-Men 3 to be released in Phase 9. It is also worth pointing out that a third X-Men film could also lead into an even bigger team-up film, such as another Avengers flick.
Avengers 7

As mentioned above, if an X-Men trilogy were to take place within the Mutant Saga, with the third movie coming in the final phase of the saga, it could lead straight into an Avengers film.
The MCU has always capped off a saga with an Avengers movie. The Infinity Saga ended with Avengers: Endgame, and the Multiverse Saga will end with Avengers: Secret Wars (find out all 14 confirmed cast members for Secret Wars here).
If the next saga focuses on Mutants and the X-Men extremely heavily, it is possible that the next Avengers film won't be released until the end of the next saga, which would be the end of Phase 9. However, it is also possible that multiple Avengers movies could be released within the next saga, so Marvel Studios may take a similar approach to what it is doing for the Multiverse Saga and release two Avengers movies in Phase 9.
Spider-Man 6

It is no secret that Spider-Man is one of the biggest heroes in Marvel history, and that he is still making a tremendous impact with fans in the MCU. For reference, Spider-Man: No Way Home grossed nearly $2 billion worldwide.
Spider-Man 4 has been confirmed to release in 2026 as a part of Phase 6. After that, the web-slinger's future is uncertain, but due to how popular he is, Marvel will want Spider-Man around for years to come.
Most likely, Spider-Man 5 will be worked into Phase 7 or Phase 8. If that is the case, fans can likely expect Spider-Man 6 to follow in Phase 9, releasing sometime before the Avengers film that will likely bring that Phase and saga to an end (just as Spider-Man 4 is doing with Phase 6 and the Multiverse Saga).
However, due to recent comments, Tom Holland may not be as interested in playing Spider-Man as he once was, so the actor's future in the franchise may not be as concrete as it once was.