According to the WWDC Keynote they are working with the FIDO Alliance on it: https://fidoalliance.org/

FIDO2/WebAuthN

Under the covers, this is webauthn, which is based on FIDO2/U2F. I knew it was webauthn as soon as I read "relying party" and the two keypairs.

Comment from the presentation: “Worked with fido alliance to work across platforms”.