Nah, they just come with their own external dac that plugs in with usb. The headphones themselves are 3.5mm.

They are super high impedance though so it's probably safe to... pretend they are usb only unless plugged into some decent audio equipment. I wouldn't expect much success plugging directly into a phone or something.

Used to spend a lot of time reading meta.stackoverflow (looked an awful lot like work at a quick glance). The sentiment from the question answerer side is something like: "I've answered this exact question 100s of times, why won't anyone search". Then this expands into enough irritation that you get a closing frenzy and similar sounding questions get caught in the cross hairs. And then everyone's mad. (plus a sprinkle of people who are just assholes on top of that)

This comment and all the responses to it so far are super cathartic. The cherry on top of all of this is the constant impression that, no, you're the crazy one. So not being entirely alone is nice.

This project was started recently-ish and implies reverse engineering is the most important part. https://librephone.fsf.org/faq Haven't seen much else listed out.