FX gave the show an additional episode in season 2, making what was initially a 10 episode season an 11 episode season. The reason behind this was that at some point in the season so many scenes were shot that ended up on the cutting room floor so as to not have 60+ minute episodes. Noah Hawley asked FX to let him have an extra episode to use a lot of the material that he deemed necessary for the story.
On February 4, 2019, it was announced that the show's third season will be its last, showrunner Noah Hawley always planned for the series to run for only three seasons and the decision to end it now comes as a result of him and the network wanting to close the story the way he always intended.
Noah Hawley had hinted at the possibility of Charles Xavier appearing in the series ever since season one. Patrick Stewart had said that he would "absolutely 100%" reprise his role on the show if given the chance despite previously claiming that Logan (2017) would be his last time portraying the character. However, Hawley decided to focus on a much younger Xavier and Harry Lloyd was cast instead. Hawley had also strongly considered having James McAvoy reprise his role from the films as well, but it was decided that casting him would be "too expensive".
In one of the episodes as Cary Loudermilk (Bill Irwin) meets the man in the diving suit (Oliver Bird), he greets him in several languages. This is a reference to the book "Twenty Thousand Leagues Under the Sea" by Jules Verne, where Professor Pierre Aronnax also greets Captain Nemo in several languages, not knowing what language he can speak.
The show is part of the X-Men cinematic universe as it connects to its future films while acting as a standalone series. However, it is hinted that this story exists in its own universe.