Finality Thresholds and Fees

In CCTP V2, finality thresholds allow integrators to specify the level of confirmation required before an offchain attestation is issued, while fees support processing Fast Transfers at faster-than-finality levels.

CCTP V2 introduces the concept of a finality threshold, which provides a chain-agnostic representation of the confirmation level for a given attestation.

In CCTP V2, each message specifies a minFinalityThreshold. This threshold indicates the minimum level of confirmation required for Circle's attestation service (Iris) to attest to the message. Iris will not attest to a message at a confirmation level below the specified minimum threshold. This allows applications to enforce a desired level of finality before acting on an attestation on the destination chain.

CCTP V2 defines the following finality thresholds:

• Messages with a minFinalityThreshold of 1000 or lower are considered Fast messages. These messages are eligible for fast attestation at the confirmed level by Iris.
• Messages with a minFinalityThreshold of 2000 are considered Standard messages. These messages are attested to at the finalized level by Iris.

CCTP V2 introduces fee collection to support Fast Transfer at faster-than-finality levels. The fee for CCTP V2 Fast Transfer should be retrieved via API call prior to transaction execution and will be collected on USDC mint onchain.

• If the maxFee set by the user is lower than the fee determined by Circle, the Fast Transfer will revert to a Standard Transfer, and no fee will be charged.
• If the maxFee is high enough, according to Circle's specified fee rate, a fee will be charged based on Circle's specified fee rate. The fee will be reflected in the feeExecuted field of the destination message, and deducted from the minted amount.