Ulrich Mueller <ulm@gentoo.org> writes:

Any special reason why this is .tar.gz, and not .tar.xz like all other
files in the directory? (I am asking because with .gz it will need an
additional case distinction in the Gentoo ebuild.)

I've uploaded an .tar.xz file now too, for your benefit:

https://alpha.gnu.org/gnu/emacs/pretest/emacs-28.3-rc1.tar.xz
https://alpha.gnu.org/gnu/emacs/pretest/emacs-28.3-rc1.tar.xz.sig

And here are the checksums:

$ sha1sum emacs-28.3-rc1.tar.xz
9d579dfc5e724d3473c52d073953281de4515726 emacs-28.3-rc1.tar.xz
$ sha256sum emacs-28.3-rc1.tar.xz
41c53433c8dc49bd017f421e09c97eda4e046f34967c872bec80b3495dfaa933
emacs-28.3-rc1.tar.xz