To use mirror.yandex.ru/mirrors/guix as a Guix substituter, pass the appropriate flag:
guix $command --substitute-urls="https://mirror.yandex.ru/mirrors/guix"
Or add it to your system configuration:
(substitute-urls (cons "https://mirror.yandex.ru/mirrors/guix"
%default-substitute-urls))
This mirror provides cached Guix substitutes (pre-built packages) from upstream (bordeaux.guix.gnu.org). All packages are signed by upstream, not by us. You must have the standard Guix signing key configured.
Recently built packages are cached actively. Everything else is cached lazily from upstream when requested.
For more details, see the official Guix manual section on substitute servers.