This post does not do Nix justice, as it only references the extensional model of Nix. In the PhD of Eelco Dolstra, the extensional model (chapter 5) describes derivations with identity based on their inputs, while the intentional model (chapter 6) describes derivations with identity based on their outputs [1]. Due to the complexity of the intentional model, the extensional model has been the initially used one. The upgrade to content addressed derivations is ongoing (see blog posts via Tweag for an intro [2]).

> Neither Nix or NixOS gives you these guarantees.

With content addressed derivations you can guarantee that any party can recreate bit-by-bit identical copies of derivations, meaning that Nix can guarantee reproducibility.

Beta testing of content addressability in Nix started in May 2021 [3].

[1] https://edolstra.github.io/pubs/phd-thesis.pdf

[2] https://www.tweag.io/blog/2020-09-10-nix-cas/

[3] https://discourse.nixos.org/t/content-addressed-nix-call-for...