Fedora releases every six months. RHEL has a major release every three years, with minor releases every six months.
The major release of RHEL is usually forked from a Fedora version about a year before the major release, so with some exceptions software versions tend to be about a year behind those in a Fedora release initially, and then as RH backports patches rather than revving versions, drifts further.
It's the patches and smaller updates — and new hardware enablement in the full-support phase — that will be landing in CentOS Stream. Previously, this stuff was developed internally and only released to the world at the minor-release drop every six months. Now, it'll be developed in a shared space. So what you'll have in CentOS Stream is whatever is intended to ship in a RHEL minor update within six months.
There may occasionally be a situation where an update introduces bugs into Stream that would have been caught by QA before a public minor RHEL release and subsequent CentOS Linux rebuild. But I don't actually expect that to happen enough to worry about in any case where you can justify not paying for actual supported RHEL in the first place.