The FIDO2 specification states that an Authenticator Attestation GUID (AAGUID) must be provided during attestation. An AAGUID is a 128-bit identifier indicating the type of the authenticator. Authenticators with the same capabilities and firmware - such as the YubiKey 5 series devices without NFC - can share the same AAGUID.

New AAGUIDs are issued for new YubiKey products which support FIDO2, or when existing YubiKey products have FIDO2 features added or removed.

For the current AAGUIDs for all devices in the YubiKey 5 FIPS Series, see YubiKey Hardware FIDO2 AAGUIDs.