I’d argue gen 3 is 3.5mm.
There was brushed stainless steel for a few years, then in late 2019 they transitioned to the powder coated finish.
Then Spring 2020 they started offering with 3.5mm BUT most importantly revised pads, making them less ethereal and more warm/ rich and a bit more in your face.
The old pads sound better imho, they sound notably more spacious, but bass is less punchy. Thankfully a bass shelf eq fixes everything.
I’ve owned 3 different Susvara (warranties) and handled 2 more.
Have also A/B’d recently the 2.5 and 3.5 and well, the pads are what make the difference and I prefer the older series personally for its more speaker-like presentation.