As with all other Debian development, we target the 'unstable' distribution for packaging work (similar to git HEAD). Packages eventually migrate from 'unstable' to the 'testing' distribution once they pass certain checks. And when Debian is ready for a new release, 'testing' will basically be tagged as '13 (trixie)'.
Ubuntu periodically syncs their packages from Debian 'unstable', so eventually they will have they same packages that Debian has.
Either way, we realize that running bleeding-edge distributions is probably not for everyone, so we intend to provide backports for both Debian and Ubuntu. Hence why I said earlier that eventually, it shouldn't matter. With "eventually" being sometime in the next few months.
(Site note: our own PyTorch does not yet ROCm support, we're still working on a few dependencies.)