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]?

[0] https://linuxiac.com/rocky-linux-confirmed-to-remain-fully-c...

[1] https://rockylinux.org/news/keeping-open-source-open