It's already operational on the Hornet.
Raytheon Intelligence & Space (RI&S) has successfully flown its pre-production APG-79(V)4 Active Electronically Scanned Array (AESA) radar system on a US...
www.defenseadvancement.com
The F-22 MLU could also get GaN over the next few years. I'd actually argue that the F-35's new GaN radar will be a derivative of what's been developed for the F-22.
Russia and China will get operational ones soon. The UK version of the Typhoon should also skip straight to GaN with Radar 2, it will apparently have both GaAs and GaN.
So all three countries will operate GaN long before France and India, which is also why I am a little bit disappointed with the Rafale F4.2.
In India's case, we are very likely to start building our first GaN prototype radar this year.