Hi Steve
SAP Sourcing/CLM is the official SAP On Premise solution for Strategic Sourcing and CLM, and as you mentioned Ariba is the cloud counterpart.
Ariba OnPremise is not being sold as a net new offering but instead is providing releases and fixes, purely from a maintenance point of view. New functionality is implemented based on a customer driven functionality perspective. This service is provided to existing customers only.
Please let us know if you have further questions.
Thanks
Amish