let
  date = "2025-02-02";
  rev = "3a228057f5b619feb3186e986dbe76278d707b6e";
  sha256 = "0iqla32cwy147lx1jw84174qkf8jyd912vxqjfgggyil1k8fix66";
in
builtins.trace "(Using pinned Nixpkgs at ${rev} from ${date} nixos-unstable)" import (fetchTarball {
  url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
  inherit sha256;
})