Nix 2.28 – 2.34 (bridge)

Updated

September 12, 2026

Area	Change
Fetchers	Stricter NAR hash mismatches; prefer SRI `hash = "sha256-…"` over legacy `sha256`.
Flakes	Source trees copied into the store more lazily (completed in 2.35).
`nix store`	`diff-closures`, `copy`, `ping` remain the daily ops set.

Pin nixos-25.11 only to read old machines. Do not start new desk hosts there: it reached EOL on 2026-06-30.

Nix 2.35

Area	Change
Flake sources	Copied to the store lazily; unused flake files are not hashed into evaluation unless needed.
Sandbox	FreeBSD jail sandboxing; Linux sandbox unchanged.
Installer	Current upstream installer ships 2.35.2 (2026-08).
Security	Recursive-nix advisory fix from the 2.35.0 series.

Key feature — current CLI on a 26.05 host

Stock 26.05 may print nix (Nix) 2.34.x. For this book’s 2.35+ baseline, install the upstream Nix installer on foreign Linux/macOS, or set nix.package = pkgs.nixVersions.latest; (or nix_2_35) on NixOS. Then:

nix --version
nix flake metadata github:NixOS/nixpkgs/nixos-26.05

Output (shape, after pinning 2.35):

nix (Nix) 2.35.2
Resolved URL:  github:NixOS/nixpkgs/nixos-26.05

NixOS 25.05 / 25.11

25.05 and 25.11 are previous stables. 25.11 “Xantusia” is deprecated (EOL 2026-06-30). If system.stateVersion is "25.11", leave it and move the flake input to nixos-26.05.

NixOS 26.05 — Yarara

Area	Change
Support	Bugfix/security until 2026-12-31.
Initrd	Stage-1 systemd initrd is the default (not the old scripted initrd).
Toolchain	GCC 15; GNOME 50 on desktop ISOs.
Nix	Channel ships Nix 2.34; book CLI baseline remains 2.35+ (installer or `nix.package`).
Modules	New options; confirm names with `nixos-option` if a 24.11 snippet fails eval.

Key feature — pin 26.05 in the desk flake

Save as flake.nix:

# flake.nix
{
  description = "Desk workstation on NixOS 26.05";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-26.05";

  outputs = { self, nixpkgs }: {
    nixosConfigurations.desk-workstation = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        {
          networking.hostName = "desk-workstation";
          system.stateVersion = "26.05";
        }
      ];
    };
  };
}

nix flake metadata
sudo nixos-rebuild dry-build --flake .#desk-workstation

Quick-Reference Matrix

The table below maps each NixOS release to the Nix CLI it ships and highlights the single most operationally significant change per pair.

NixOS Release	Nix Version Shipped	Most Impactful Addition
23.05 Stoat	2.13	Flakes opt-in stable via `experimental-features`
23.11 Tapir	2.18	`nix flake metadata` improvements; `--log-format` for CI
24.05 Uakari	2.22	`nix build --rebuild` reproducibility check; systemd initrd opt-in
24.11 Vicuna	2.24	`nix store diff-closures` stable; `services.openssh.settings.AllowGroups`
25.05	2.28	`nix flake check` / fetch-tree hardening; module cleanups
25.11 Xantusia	2.31	EOL 2026-06-30; last train before Yarara
26.05 Yarara	2.34 (pin 2.35+)	Current baseline; systemd stage-1 initrd default; GCC 15

Nix 2.19–2.34 intermediate releases are available via pkgs.nixVersions even when the channel ships another version. Pin only when you need a CLI feature the channel does not have yet:

# configuration.nix  (pin Nix version independently of channel)
{ pkgs, ... }:
{
  nix.package = pkgs.nixVersions.latest; # or pkgs.nixVersions.nix_2_35
}