Hello,
Thank you for contacting Sighthound support. There is only a one time fee for licenses which are valid forever. We do have a Support and Upgrade subscription which you automatically get 1 year free. This allows you to upgrade any major versions of Sighthound. This is not mandatory and if you are happy with your current build, you can run it forever. You can find more information about this subscription at the link below:
https://www.sighthound.com/support/abou ... scriptionsPlease let us know if you have any other questions or concerns about this, thank you!
Regards,
-Kevin