C'est une des quatre inputs suivantes:

  inputs.released-nixpkgs-unstable.url = "nixpkgs/nixos-unstable";
  inputs.released-nixpkgs-stable.url = "nixpkgs/nixos-23.05";
  inputs.released-nix-unstable.url = "github:nixos/nix/master";
  inputs.released-nix-stable.url = "github:nixos/nix/latest-release";