{
  description = "Chris's NixOS machines";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";
    # Only the existing hosts use this for apps previously taken from unstable.
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixos-unstable";
    nixos-hardware = {
      url = "github:NixOS/nixos-hardware";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs =
    {
      nixpkgs,
      nixpkgs-unstable,
      nixos-hardware,
      ...
    }:
    {
      # Build the CLI packages separately before switching a host.
      packages.x86_64-linux = import ./packages/ai-cli.nix {
        pkgs = import nixpkgs {
          system = "x86_64-linux";
          config.allowUnfree = true;
        };
      };

      nixosConfigurations = {
        t450s = nixpkgs.lib.nixosSystem {
          specialArgs.unstable = import nixpkgs-unstable {
            system = "x86_64-linux";
            config.allowUnfree = true;
          };
          modules = [ ./hosts/t450s/configuration.nix ];
        };
        x1eg2 = nixpkgs.lib.nixosSystem {
          specialArgs.unstable = import nixpkgs-unstable {
            system = "x86_64-linux";
            config.allowUnfree = true;
          };
          modules = [ ./hosts/x1eg2/configuration.nix ];
        };
        framework = nixpkgs.lib.nixosSystem {
          modules = [
            nixos-hardware.nixosModules.framework-11th-gen-intel
            ./hosts/framework/configuration.nix
          ];
        };
      };
    };
}