The new version breaks binary compatability with 8.0, hence the new version number.
New versions of glibc, and a new POSIX compliant threads implimentation.
Note this is version "9" not "9.0" - RH seem to regard this as stable, hence not point zero.
There is not a package list yet, but looking at the package list for Phoebe, the beta, gives a good idea of what's inside.
Non-RHN users will get the release one week later.
Red Hat release quarterly results this month.
Ten years of Red Hat this month too."