It was announced back in June 2014, that Rian Johnson would be creating a treatment for Derek Connolly and Colin Trevorrow, the writers of Episode IX, but now that is now no longer the case. Trevorrow and Connolly will be writing the follow-up to Star Wars: The Last Jedi without any input from Rian Johnson. Trevorrow and Connolly gained acclaim with their surprise indie-sci feature Safety Not Guaranteed, which propelled them to project like Jurassic World and Kong: Skull Island. Both films achieved box office success, but most critics thought the script was the weaker part of both films.
@mattpeto That's old info, I haven't been involved in writing IX.
— Rian Johnson (@rianjohnson) April 24, 2017