Exstream version history

Hi, Can anyone help with the details of OTExstream version history ?

We have a legacy version 16.6.31 and we are trying to find out the latest version supported for a non-cloud migration.

If I understand correctly the latest version (23) supports only a SaaS model, is that correct?

SaaS migration is a long-term target for us, but would like to migrate to the latest on-prem supported version first.

Thank you!