According to this other article [0] they still aim for 1:1 compatibility with RHEL, and not Stream. I also don't see any mention of Stream in the Rocky 9 release notes.
EDIT: I wonder if Rocky is still following their original plans to leverage rented VMs [1]?
https://www.zdnet.com/article/rocky-linux-9-arrives-with-eve...
That says they pull from CentOS Stream, which I think is upstream from RHEL.