{
  inputs,
  system,
  ...
} @ args: {
  nixpkgs.channels.default = rec {
    default = upkgs;
    # nixpkgs-unstable
    upkgs = {
      inherit system;
      source = inputs.nixpkgs-unstable;
      overlays = with inputs; [
        cachyos.overlays.pinned
        millennium.overlays.default

        # XXX: WARNING: TODO: cerulean will
        (import ./overlays.nix args)
      ];

      config.allowUnfree = true;
    };
    # nixpkgs-staging
    spkgs = {
      inherit system;
      source = inputs.nixpkgs-staging;
      overlays = [];
      config.allowUnfree = true;
    };
  };
}