The film was originally set up as a two-parter. Simon Kinberg wanted to adapt faithfully after botching the first “Dark Phoenix”. 20th Century Fox changed its mind and ordered just one movie. Kinberg re-wrote the script to accommodate the change.
Fox used test screenings to help determine which parts of the film needed to be reworked and it was Kinberg’s ending that changed the most.
Fox gave its pre-summer season February slot to “Alita” and forced “Dark Phoenix” into the summer. Fox Studios CEO Snider was under pressure from “Alita: Battle Angel” producer James Cameron (studio’s most prized director).