How channels work
nixpkgs uses the channels feature of nix.
nixpkgs is distributed for users of Nix on non-NixOS distributions through the channel nixpkgs-unstable. Users of NixOS generally use one of the nixos-* channels,
e.g. nixos-22.11, which includes all packages and modules for the stable NixOS
22.11. Stable NixOS releases are generally only given
security updates. More up to date packages and modules are available via the nixos-unstable channel.
Both nixos-unstable and nixpkgs-unstable follow the master branch of the
nixpkgs repository, although both do lag the master branch by generally a couple of days. Updates to a channel are
distributed as soon as all tests for that channel pass, e.g. this table shows the status of tests for the nixpkgs-unstable channel.
The tests are conducted by a cluster called Hydra,
which also builds binary packages from the Nix expressions in Nixpkgs for x86_64-linux, aarch64-linux, x86_64-darwin and aarch64-darwin.
The binaries are made available via a binary cache.
The current Nix expressions of the channels are available in the nixpkgs repository in branches
that correspond to the channel names (e.g. nixos-22.11-small).