The situation with the Fox X-Men films and streaming in the US is a complicated one, as Fox and HBO have an on-going deal that began in 2012 and runs until 2022 for their movies, which is why if you look at the recently-launched HBO Max it’s filled with older Fox movies; many of which would fit in with Disney+.
Among those movies are the Fox X-Men films, but now some of them will arrive on Disney+ in the US (after being available in other countries).
Not all of them will arrive, but this is what’s coming soon:
July 10th: X-Men: Days of Future Past
July 17th: X-Men: Apocalypse
August 7th: X-Men
September 4th: The Wolverine
In addition, the only Fantastic Four movie that hasn’t streamed on the service (the original from 2005) will be added on August 28th. The 2015 one is currently on Disney+, and Rise of the Silver Surfer was just recently removed.