The CentOS Stream 9 content has been available quite a while now. They just made it more visible last week.
AlmaLinux  is built from released sources of RHEL 8. There is no RHEL 9 yet, so nothing to build from. Then again, AlmaLinux had a beta for 8.5 briefly before official release of RHEL 8.5. Nevertheless, the official AlmaLinux 9 release is bound to official release of RHEL 9. Soon After™, I presume.
In the meantime, isn’t CentOS Stream 9 (C9S) a decent technology preview of the future (RH)EL9 content?
We all know that (RH)EL does not provide wide selection of alternatives, like Desktop Environments. It took a good while for EPEL to populate after RHEL 8 was released. That seems to have improved and there are even beginnings of epel-next for C9S. Still, unless you are content with what will be in RHEL 9, you would have to wait to official release of RHEL 9 and then some before you could use AlmaLinux 9 “in production” (presuming it appears practically simultaneously with RHEL 9).
As anecdote, NVidia drivers were not in main ELRepo repository the moment when RHEL 8.5 released. Not even when AlmaLinux 8.5 was released. A trivial “dnf upgrade” was not possible immediately, but after a couple days.