MDS v3 publishes a BLOB at https://mds3.fidoalliance.org/, a JWT signed with a certificate chained to the FIDO root, containing one entry per authenticator model with its metadata statement and status reports such as FIDO_CERTIFIED_L1 or REVOKED. Relying parties download it periodically, verify the signature and use the entry matching the AAGUID to validate an attestation certificate chain and enforce policy.
It covers certified hardware authenticators well; synced passkey providers mostly do not send attestation at all. Enterprises often combine MDS with an allowlist of AAGUIDs and their own device management data.