The whole beauty of Nix was that it was incredibly pragmatic to achieve “reproducibility”, which is quite an overloaded term. The default model for Nix is the intensional-model which is input-addressed: the hash of a store path is derived from the recipe (derivation) that produced it, and not the bytes that came out of it. In that framing Nix achieves repeatability. Nix, by default, was never bit-for-bit reproducible.1 Nix has a ca-derivations feature that makes the output path a hash of the output bytes, which is a different model (extensional-model). ↩