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Overview

Finality refers to the point at which a blockchain transaction becomes irreversible. CCTP uses finality thresholds to determine when it’s safe to issue attestations for cross-chain transfers.

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Finality Thresholds

CCTP V2 supports two finality threshold values:

1000 - Fast Transfer

Lower threshold for faster attestations with a fee

2000 - Standard Transfer

Higher threshold for secure, fee-free transfers

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Fast Transfer (Threshold 1000)

Characteristics:
  • Attestation time: ~8-20 seconds
  • Fee: 1-14 basis points depending on source chain
  • Security level: Lower finality threshold
  • Use case: Time-sensitive transfers where speed is critical
// From transfer.go:234-241
if transferType == TransferTypeFast {
    minFinalityThreshold = 1000
    transferTypeLabel = "Fast Transfer"
} else {
    minFinalityThreshold = 2000
    transferTypeLabel = "Standard Transfer"
}

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Standard Transfer (Threshold 2000)

Characteristics:
  • Attestation time: ~13-19 minutes for most chains, ~8 seconds for instant finality chains
  • Fee: No fee (0 bps)
  • Security level: Higher finality threshold
  • Use case: Cost-sensitive transfers with no time constraints

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Instant Finality Chains

Some chains have instant finality, meaning transactions are final immediately after confirmation. For these chains, Standard Transfer is just as fast as Fast Transfer.

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Mainnet Instant Finality Chains

  • Avalanche (Domain 1) - Avalanche consensus provides instant finality
  • Polygon PoS (Domain 7) - PoS mechanism with fast finality
  • Sonic (Domain 13) - Instant finality design
  • Sei (Domain 16) - Optimistic parallelization with instant finality
  • XDC (Domain 18) - XDPoS consensus with instant finality
  • HyperEVM (Domain 19) - Instant finality architecture

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Testnet Instant Finality Chains

  • Avalanche Fuji (Domain 1)
  • Polygon PoS Amoy (Domain 7)
  • Sonic Testnet (Domain 13)
  • Sei Testnet (Domain 16)
  • XDC Apothem (Domain 18)
  • HyperEVM Testnet (Domain 19)
  • Arc Testnet (Domain 26)
Fast Transfer is not available when instant finality chains are the source, as Standard Transfer already provides ~8 second attestations with no fee.

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How Finality Works

1

Burn transaction confirmed

User burns USDC on the source chain via TokenMessengerV2 contract
2

Finality threshold reached

The source chain waits for the specified finality threshold (1000 or 2000) to be reached
3

Attestation issued

Circle’s Iris service validates the burn and issues an attestation
4

Attestation retrieved

The SDK polls the Iris API to retrieve the attestation
5

Mint transaction

The attestation is submitted to the destination chain to mint USDC

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Attestation Timing

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Fast Transfer Timing

// From client.go:266-270
func EstimatedAttestationTime(instantFinality bool) time.Duration {
    if instantFinality {
        return 10 * time.Second // ~8-10 seconds for instant finality
    }
    return 15 * time.Second // ~8-20 seconds for Fast Transfer
}

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Standard Transfer Timing

  • Regular EVM chains: ~13-19 minutes
  • Instant finality chains: ~8-10 seconds

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Auto-Selection Logic

When using TransferTypeAuto, the SDK automatically selects the optimal transfer type: 
// From transfer.go:222-230
transferType := t.params.TransferType
if transferType == "" || transferType == TransferTypeAuto {
    if t.params.SourceChain.InstantFinality {
        transferType = TransferTypeStandard
        log.Info("Auto-selected Standard Transfer (instant finality chain)")
    } else {
        transferType = TransferTypeFast
        log.Info("Auto-selected Fast Transfer")
    }
}
Logic:
  • Instant finality source chain → Standard Transfer (no fee, same speed)
  • Regular EVM source chain → Fast Transfer (faster attestation with fee)

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Checking Chain Finality

You can check if a chain has instant finality: 
import "github.com/circlefin/cctp-go"

chain, err := cctp.GetChainByName(cctp.Avalanche, false)
if err != nil {
    panic(err)
}

if chain.InstantFinality {
    fmt.Println("This chain has instant finality")
    fmt.Println("Standard Transfer will be fast (~8 seconds)")
} else {
    fmt.Println("This chain uses probabilistic finality")
    fmt.Println("Consider Fast Transfer for speed (~8-20 seconds)")
}

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Comparison Table

Chain TypeFast TransferStandard Transfer
Regular EVM~8-20 seconds (with fee)~13-19 minutes (no fee)
Instant FinalityNot available~8-10 seconds (no fee)

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Best Practices

  • Time-sensitive applications (trading, arbitrage)
  • Source chain is not an instant finality chain
  • Fee is acceptable for your use case
  • Cost is the primary concern
  • Source chain has instant finality
  • You can wait 13-19 minutes for regular EVM chains
  • Building a general-purpose application
  • Want the SDK to choose optimally based on chain capabilities
  • Need consistent behavior across different chains

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See Also

Transfer Types

Learn about Fast and Standard transfers

Supported Chains

View all chains and their finality characteristics

Fees

Understand fee calculation

IrisClient

Attestation polling API

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