So the real versions here is in the `import <nixpkgs> {};` You need to pin it to a specific version or even commit from nixpkgs github repo. So instead of that,

So the real versions here is in the `import <nixpkgs> {};` You need to pin it to a specific version or even commit from nixpkgs github repo. So instead of that, you can find the commit that has all your desired versions and pin it that way. with import (builtins.fetchTarball https://github.com/NixOS/nixpkgs/archive/9a5f7b1630c138a82cb9ae0d6a513c4358c1dc10.tar.gz https://github.com/NixOS/nixpkgs/archive/9a5f7b1630c138a82cb...) {}; This way, all your versions of packages will be pinned to this specific revision, and you can also use multiple revisions at the same time.