Updates are committed to the stable nixpkgs branch. These then propagate through the channel. NixOS has a configuration option to enable automatic upgrades[1],

Updates are committed to the stable nixpkgs branch. These then propagate through the channel. NixOS has a configuration option to enable automatic upgrades[1], which periodically pulls the latest nixpkgs checkout from the channel you're following, rebuilds the system, and switches to that configuration. [1]: https://nixos.org/nixos/manual/#sec-upgrading-automatic https://nixos.org/nixos/manual/#sec-upgrading-automatic