depot/third_party/home-manager/docs/manual/faq/unstable.md

How do I install packages from Nixpkgs unstable?

If you are using a stable version of Nixpkgs but would like to install some particular packages from Nixpkgs unstable -- or some other channel -- then you can import the unstable Nixpkgs and refer to its packages within your configuration. Something like

{ pkgs, config, ... }:

let

  pkgsUnstable = import <nixpkgs-unstable> {};

in

{
  home.packages = [
    pkgsUnstable.foo
  ];

  # …
}

should work provided you have a Nix channel called nixpkgs-unstable.

You can add the nixpkgs-unstable channel by running

$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable nixpkgs-unstable
$ nix-channel --update

Note, the package will not be affected by any package overrides, overlays, etc.