here is the supported paths to update to the latest versions. https://docs.splunk.com/Documentation/Splunk/latest/Installation/HowtoupgradeSplunk
Currently the newest version is 9.0.1, but based on that “one over” policy also 8.2 -> 9.1 should agreed option.
As there is no 8.3 version you could go directly from 8.2.x to 9.1.x when it comes out sometime on next year. That will be valid way unless Splunk change their policy. On clustered environments you should/could do a live update “without service breaks”.
When they release 9.1 that will be told on installation guide.