# I am confused about the reproducibility of a system through flakes

**URL:** https://discourse.nixos.org/t/i-am-confused-about-the-reproducibility-of-a-system-through-flakes/78974
**Category:** Help
**Created:** [July 16, 2026, 7:44am UTC](https://discourse.nixos.org/t/i-am-confused-about-the-reproducibility-of-a-system-through-flakes/78974 "2026-07-16T07:44:23Z")
**Posts on this page:** 1
**Showing post:** 9

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### Author: ![withakay](https://discourse.nixos.org/letter_avatar_proxy/v4/letter/w/f475e1/32.png) [@withakay](https://discourse.nixos.org/u/withakay)
#### Post date: [July 16, 2026, 1:55pm UTC](https://discourse.nixos.org/t/i-am-confused-about-the-reproducibility-of-a-system-through-flakes/78974/9 "2026-07-16T13:55:22Z")

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> [@frost](#):
>
> Derivations, by specifying expected hashes for their requirements (such as downloaded source code), and being built in isolated environments, should be bit-by-bit reproducible, such that two people building the same version of the same package can reproduce the exact same result (ignoring, for example, `-march=native` optimisation or similar hardware-linked variance).

Bit-for-bit reproducibility is a very high bar, and while projects like [https://reproducible.nixos.org/](https://reproducible.nixos.org/) attempt to tackle this and binary caches can hide/mitigate/shim bit-for-bit-style reproducibility, the use of nix alone is not sufficient to claim bit-for-bit style repro, especially because many build chains and software are not written to be easily bit-for-bit repro. See ["NixOS is not reproducible"](https://discourse.nixos.org/t/nixos-is-not-reproducible/42688) for more details and perhaps a better place to actually have the discussion if more commentary is important. I’m only commenting in this thread because I think as a community it does a disservice to advertise claims that later do not prove out. That can cause a lot of loss of faith in the ecosystem.

Nix does provides dependency-graph reproducibility, as you note, which is already great for most practical purposes and very hard to achieve in other ecosystems. A great win! Definitely a huge reason to use nix, and I don’t see a better tool currently.

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