For reference in case the above example stops being available or changes, this example is permanently available since time of writing: https://rawcdn.githack.com/immersive-web/model-element/ed579b5ad3fdca3bca2805e182624a23d367b534/examples/assets/FlightHelmet.usdz

I can confirm, it doesn't work right now. With this example, https://raw.githack.com/immersive-web/model-element/main/examples/index.html in macOS M1 I get a blank rectangle: and in visionOS I get the image fallback: I do see that model.constructor is HTMLModelElement, and model.getCamera() eventually gives the error Unhandled Promise Rejection: undefined so the API is there, just not working yet It is experimental behind a flag, so the WebKit team may still be ironing out the details.