How to install prerelease package versions (particularly Emacs)

[Jorge]

Hi.  I use Spacemacs v.0.300.0 (develop) atop Emacs 26.0.91.  I compile
Emacs 26 locally and stow it with GNU Stow.  I would prefer to get Emacs
26 from Guix, which would be more automatic and would come configured to
work with Guix-installed Emacs packages.  So is Emacs 26 available from
Guix?  Unfortunately ~guix package --show=emacs~ only reports version
25.3, but maybe there is a non intuitive way to get Emacs 26.

Regards

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