I don't know where you heard that? The source code for Red Hat's RISC-V developer preview will be released alongside the binaries, on 1st June. However almost all of it is already in CentOS Stream 10 and you can browse it here: https://gitlab.com/redhat/centos-stream There are a few patched packages (and quite a large kernel patch), which is what we'll be releasing into a separate git repo when the developer preview is actually released.

We've been building the RISC-V port from a combination of Fedora and CentOS Stream sources--the same as the core operating system--since early 2024.

A lot of RISC-V support was already in F40 (which EL10 is cut from), so the rest was largely backporting and integrating into RHEL, which again, we've been tracking since CentOS Stream 10 was branched from Fedora last year.