To people looking for an archive of the XZ code, you might want to check out https://tukaani.org/xz-backdoor/ which links to https://git.tukaani.org/. GitHub is not the only source of truth, although meta information about the Pull Requests is locked in to this silo.
@Codeberg Many thanks for your work on openess. It's another proof that git history is not sufficient and we cannot tolerate a locked silo like Github. PR, issues, comments and everything else are an essential part of the repository, the code is not enough.