Microsoft only announced GDR2 for the Lumia 830 and 735, but it seems there is an easy way to get it for the flagship Windows Phone 8.1 handset, the Lumia 930, for the moment at least.
Simply download and sign up for the Windows Insider program on your phone, set it to Fast Track, and then check for updates in settings.
In short order Windows Phone 8.1 Update 2 will download to your handset, enabling things like Bluetooth keyboard support, the ability to pin settings, a data toggle, grouped and searchable settings and more.
From what we understand the images being downloaded were already customized for Mobile Operators, who were not bothering to roll them out. In my testing on my Lumia 930 my handset felt a lot faster, and so far it has been bug free, so it seems a relatively good idea, without all the baggage and limitations of the alpha software that is still Windows 10 Mobile Technical Preview.
It seems not getting Windows 10 Mobile TP on the 930 was a blessing in disguise in the end.