A periodic report from an independent auditor confirming that a stablecoin's reserves match its outstanding supply.
A reserves attestation is a report from a third-party auditor (or accounting firm) confirming that a fiat-backed stablecoin issuer holds sufficient reserves to back its outstanding supply, with a breakdown of what those reserves consist of. Circle publishes monthly attestations for USDC; Tether publishes quarterly attestations for USDT. Attestations are weaker than a full audit — they usually attest to a point-in-time snapshot, not to the operational controls of the issuer.