Temporal doesn't run your AI compute for you, you bring your own hardware on prem or in your cloud account or whereever. Their SaaS is a control plane to coordinate and orchestrate the workers.
Temporal is fully open source, you can run the entire thing on your laptop or your own server. People pay for the SaaS anyway, because dealing with the distributed computing problems is hard.
(There are some other projects inspired by Temporal as well, but if you want to run something in-house, you're probably funding a minimum of 2-3 engineers to handle on-call, and for that price the SaaS is competitive).