> ## Documentation Index
> Fetch the complete documentation index at: https://developers.circle.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Finality and block confirmations

> Block confirmation requirements and attestation timing for CCTP

Before signing an attestation, Circle waits for blockchain transactions to
achieve the appropriate level of transaction finality. The required finality
level depends on whether you use Fast Transfer or Standard Transfer.

* Fast Transfer: Attestations are issued after the transaction is confirmed and
  included in a block, typically in seconds. Because of the faster finality
  time, Fast Transfers are subject to a global allowance to mitigate
  reorganization risks.
* Standard Transfer: Attestations are issued after hard finality, when the
  transaction is unlikely to be reversed by a chain reorganization, typically in
  minutes.

## Fast Transfer attestation times

The table below shows the average time for attestations to become available when
using Fast Transfer (`minFinalityThreshold` ≤ 1000):

| Source blockchain | Block confirmations | Average time |
| ----------------- | ------------------- | ------------ |
| **Ethereum**      | 2                   | \~20 seconds |
| **Arbitrum**      | 1                   | \~8 seconds  |
| **Base**          | 1                   | \~8 seconds  |
| **Codex**         | 1                   | \~8 seconds  |
| **EDGE**          | 1                   | \~8 seconds  |
| **Ink**           | 1                   | \~8 seconds  |
| **Linea**         | 1                   | \~8 seconds  |
| **Morph**         | 1                   | \~8 seconds  |
| **OP Mainnet**    | 1                   | \~8 seconds  |
| **Plume**         | 1                   | \~8 seconds  |
| **Solana**        | 2-3                 | \~8 seconds  |
| **Starknet**      | 4                   | \~20 seconds |
| **Unichain**      | 1                   | \~8 seconds  |
| **World Chain**   | 1                   | \~8 seconds  |

<Note>
  **Blockchains without Fast Transfer:**

  Some blockchains don't support Fast Transfer as a source blockchain because
  their standard attestation times are already fast. For those
  [CCTP supported blockchains](/cctp/concepts/supported-chains-and-domains) where
  Fast Transfer is disabled as a source, use Standard Transfer instead.
</Note>

## Standard Transfer attestation times

The table below shows the average time for attestations to become available when
using Standard Transfer (`minFinalityThreshold` ≥ 2000):

| Source blockchain   | Block confirmations | Average time    |
| ------------------- | ------------------- | --------------- |
| **Ethereum**        | \~65                | \~15-19 minutes |
| **Arbitrum**        | \~65 ETH blocks     | \~15-19 minutes |
| **Arc**             | 1                   | \~0.5 seconds   |
| **Avalanche**       | 1                   | \~8 seconds     |
| **Base**            | \~65 ETH blocks     | \~15-19 minutes |
| **BNB Smart Chain** | 3                   | \~2 seconds     |
| **Codex**           | \~65 ETH blocks     | \~15-19 minutes |
| **Cronos**          | 1                   | \~0.5 seconds   |
| **EDGE**            | \~65 ETH blocks     | \~16-21 minutes |
| **HyperEVM**        | 1                   | \~5 seconds     |
| **Injective**       | 1                   | \~0.65 seconds  |
| **Ink**             | \~65 ETH blocks     | \~30 minutes    |
| **Linea**           | 1                   | \~6-32 hours    |
| **Monad**           | 1                   | \~5 seconds     |
| **Morph**           | \~65 ETH blocks     | \~20-30 minutes |
| **OP Mainnet**      | \~65 ETH blocks     | \~15-19 minutes |
| **Pharos**          | 1                   | \~7 seconds     |
| **Plume**           | \~65 ETH blocks     | \~15-19 minutes |
| **Polygon PoS**     | 2-3                 | \~8 seconds     |
| **Sei**             | 1                   | \~5 seconds     |
| **Solana**          | 32                  | \~25 seconds    |
| **Sonic**           | 1                   | \~8 seconds     |
| **Starknet**        | \~65 ETH Blocks     | \~4 to 8 hours  |
| **Stellar**         | 1                   | \~5 seconds     |
| **Unichain**        | \~65 ETH blocks     | \~15-19 minutes |
| **World Chain**     | \~65 ETH blocks     | \~15-19 minutes |
| **XDC**             | 3                   | \~10 seconds    |

## Layer 2 finality

Layer 2 (L2) blockchains built on Ethereum publish transaction data in batches
to Ethereum Layer 1. The finality characteristics of L2 chains depend on when
batches are posted and when those batches achieve finality on Ethereum L1.

<CardGroup cols={2}>
  <Card title="OP Stack chains" icon="layer-group">
    OP Stack-based chains (including Base, OP Mainnet, and World Chain) post
    state updates using [EIP-4844](https://www.eip4844.com/) blob transactions
    approximately every 15 minutes. Circle waits for the Ethereum L1 block
    containing the batch to finalize, which typically takes \~65 blocks (15-19
    minutes) after the batch is posted.
  </Card>

  <Card title="Linea" icon="clock">
    Linea has a longer finality period compared to other L2 chains. Standard
    Transfer on Linea typically requires 6-32 hours before attestations become
    available.
  </Card>

  <Card title="Starknet" icon="clock">
    The typical time to reach hard finality on Starknet is 4–8 hours, as finality
    depends on when the zk-rollup proof is posted to Ethereum and when its
    corresponding L1 block finalizes.
  </Card>
</CardGroup>

## Solana finality

Solana uses a different finality model:

<CardGroup cols={2}>
  <Card title="Fast Transfer" icon="bolt">
    Circle waits for the block to be confirmed (votes from validators
    representing over two-thirds of total stake). This typically takes 2-3
    blocks (\~8 seconds).
  </Card>

  <Card title="Standard Transfer" icon="shield-check">
    Circle waits for block finality, which takes 32 blocks (\~25 seconds).
  </Card>
</CardGroup>