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.

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.