If you have an older Sibelius (the "big" version min. Version 5) or Sibelius Ultimate with an expired upgrade plan, you will get the latest version and all upcoming updates in the next 3 years.
This upgrade can not be used if your version of Sibelius is part of a multi-user license or if you have Sibelius First / Artist.
If you already have Sibelius Ultimate with an active upgrade plan, you should instead buy the cheaper 1- or 3-year “renewal”.