Just for context to the GP, Nix channels work basically the exact same way. Or, you can do as I do, and not use channels and always specify the exact nixpkgs revision as part of your Nix file. Anyone can `nix-build chimera.nix` and get a (nearly) bit-for-bit identical build of my laptop, which is great - we don't have to have a conversation about which channel I'm on, or which rev of which channel I'm on, etc.

I can then independently rev the nixpkgs revision and either commit that, or not.