Nix Flake
Reproducible-by-default Nix project format. flake.nix + flake.lock pin all deps exactly. Stable since Nix 2.4 (2021), default in Nix 2.18+. Modern way to use Nix.
Distinct from legacy Nix: flake-lock file captures exact hashes of all input deps (nixpkgs revision, other flakes). nix build reproduces bit-perfect over months/years. Use cases: dev-shells (replacement for devcontainers), CI jobs, NixOS system config, Home Manager (dotfiles management). Conservative skeptics see flakes as experimental feature despite production use. Community Holy War: flakes vs niv vs nvfetcher vs callPackage-traditional Nix. Modern Nix usage 2024 default flakes — adoption tipping point reached.