OnePlus has finalised the model numbers of the OnePlus 9 series, but there will be no OnePlus 9 Ultra. Instead, OnePlus will be releasing just the OnePlus 9 and OnePlus 9 Pro.
https://www.notebookcheck.net/There-will-be-no-OnePlus-9-Ultra-next-year-but-the-OnePlus-9-and-OnePlus-9-Pro-are-coming.504283.0.html