BarTender service releases are always free to users of that version. For example, 10.1 SR4 is free to users of 10.1.
Please note that starting with BarTender 2016, releases between major versions will be identified as BarTender 2016 R2, BarTender 2016 R3 and so on. We will no longer refer to these as service releases, as these releases can include additional features, not just bug fixes.
Version: BarTender 2016 R8, released 2018-09-05.