Out of curiousity, i looked. From what i understand GaN radar for F-15EX is just a proposal atm. It is not clear if the E/A-18G has received the GaN APG-79(V)4 which is fitted to upgraded legacy C/D models, if there is definite confirmation i'll stand corrected but i haven't seen anything clear.
No, you are correct the GaN radar is proposed to slot in future production batches of F-15EX production (as APG-82(V)X). The E/A-18G uses the ALQ-249 jammer which utilizes GaN. The Eagle Passive Active Warning Survivability System (EPAWSS) upgrade for the F-15E and EX also uses GaN. Outside of aircraft, you have the upgraded AN/MPQ-65A for Patriot, it’s replacement the Lower-Tier Air and Missile Defense System (LTAMDS), and the AN/TPS-80 Ground/Air Task Oriented Radar all utilizing GaN technology.
My point was really that these systems are already widely adopted in US (and Chinese) service in many areas, so getting GaN on a future variant of the Su-57 isn’t really a game changing upgrade for the aircraft when looking at what the US and China currently field. Certainly Russia doesn’t have the depth of experience is using any type of AESA radar that the US and China do.