Just install the standalone Nix installer like you would on any other (non-Nix) distro (see this part of the Nix manual: https://nixos.org/nix/manual/#chap-quick-start ). Both Guix and Nix are designed to work on top of 'foreign' distros, and this includes using a standalone Nix package manager on GuixSD and a standalone Guix package manager on NixOS (or both the standalone Guix package manager and the standalone Nix package manager on top of Arch Linux, etc. etc.)