NixOS 19.09 “Loris” has been released, the twelfth stable release branch. See the release notes for details. You can get NixOS 19.09 ISOs and VirtualBox appliances from the download page. For information on how to upgrade from older release branches to 19.09, check out the manual section on upgrading.
NixOS 19.09 released
Published on Wed Oct 09 2019