In addition to numerous new and upgraded packages, this release has the following highlights: You can now pin a specific version of NixOS in your configuration.nix by setting: nixos.path = ./nixpkgs-unstable-2015-12-06/nixos; This will make NixOS re-evaluate your configuration with the modules of the specified NixOS version at the given path. For more details, see The following new services were added since the last release: services/monitoring/longview.nix When upgrading from a previous release, please be aware of the following incompatible changes: wmiiSnap has been replaced with wmii_hg, but services.xserver.windowManager.wmii.enable has been updated respectively so this only affects you if you have explicitly installed wmiiSnap. wmiimenu is removed, as it has been removed by the developers upstream. Use wimenu from the wmii-hg package. Gitit is no longer automatically added to the module list in NixOS and as such there will not be any manual entries for it. You will need to add an import statement to your NixOS configuration in order to use it, e.g. ]; } ]]> will include the Gitit service configuration options. nginx does not accept flags for enabling and disabling modules anymore. Instead it accepts modules argument, which is a list of modules to be built in. All modules now reside in nginxModules set. Example configuration: s3sync is removed, as it hasn't been developed by upstream for 4 years and only runs with ruby 1.8. For an actively-developer alternative look at tarsnap and others. ruby_1_8 has been removed as it's not supported from upstream anymore and probably contains security issues. tidy-html5 package is removed. Upstream only provided (lib)tidy5 during development, and now they went back to (lib)tidy to work as a drop-in replacement of the original package that has been unmaintained for years. You can (still) use the html-tidy package, which got updated to a stable release from this new upstream.