Quoting Carl George of CentOS/Red Hat:
so let me clear up a few things. what was just released
was rhel 9 beta, not 9.0 beta. there is a difference. the rhel 9
beta is the beta for the major version, and really amounts to being
just a minor release before .0, so think 9.-1. it does not get
updates, it’s essentially frozen. it’s based on where centos 9 stream
was like 3 months ago. c9s is now representing 9.0 ga content, so
it’s further ahead than 9 beta.r9.b is only stable in the sense that it’s frozen and
the bugs it has will stay as-is. c9s has a ton of bug fixes that r9.b
doesn’t have. many of the community contributed things we have now in
c9s missed the window for r9.b but are in c9s now so they can make it
into r9.0.