> ## Documentation Index
> Fetch the complete documentation index at: https://circle-devdocs-test-ai-codegen-component.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Cross-Chain Transfer Protocol

> Move USDC securely across blockchains and simplify user experience

## Overview

[Cross-Chain Transfer Protocol (CCTP)](https://circle.com/cctp) is a
permissionless onchain utility that facilitates USDC transfers securely between
supported blockchains via native burning and minting. Circle created CCTP to
improve capital efficiency and minimize trust assumptions when using USDC across
blockchains. CCTP enables developers to build multichain applications that allow
users to perform 1:1 transfers of USDC securely across blockchains.

<Note>
  **Tip**: Use Bridge Kit for easy crosschain transfers through CCTP.

  [Bridge Kit](/bridge-kit) is an SDK that uses CCTP as its protocol provider to let you transfer USDC between blockchains in just a few lines of code
</Note>

CCTP V2 supports both **Fast Transfer** and **Standard Transfer**, and also
integrates **Hooks** for custom logic. Fast Transfer enables USDC transfers
between blockchains at faster-than-finality speeds, reducing transfer times from
over 15 minutes to under 30 seconds across most domains. Hooks enhance
crosschain composability by allowing you to trigger automated actions
post-transfer. For more details, see the
[Hooks](/cctp/technical-guide#cctp-hooks) section.

<Note>
  **Note:** CCTP V2 uses a separate set of contracts and is not backward
  compatible with earlier versions. Developers who need to continue using
  Standard Transfer should consider upgrading to the latest CCTP version.
</Note>

## Background and Design

The following sections provide additional context on CCTP’s evolution, the
challenges it addresses, and its architectural principles. Expand any to explore
these deeper technical details.

<br />

<AccordionGroup>
  <Accordion title="Differences between CCTP V2 and CCTP V1">
    To better understand the evolution of CCTP, the following table highlights the
    key differences between CCTP V2 and CCTP V1:

    | Feature                    | CCTP V2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | CCTP V1                                                                                                                  |
    | -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------ |
    | **Finality Time**          | **Fast Transfer:** faster-than-finality, \~8-20 seconds for EVM chains <br /><br /> **Standard Transfer:** <Tooltip tip="The point at which a transaction is fully finalized on-chain and can no longer be reversed or reorganized. This ensures the highest level of security and certainty before attestation. Hard Finality requires the transaction to reach full consensus on the source blockchain, typically resulting in longer processing times.">hard finality</Tooltip>, \~13-19 minutes for Ethereum and L2 chains | **Standard Transfer:** hard finality, \~15 to 19 minutes for Ethereum and L2 chains                                      |
    | **Supported Blockchains**  | **Standard Transfer:** Arbitrum, Avalanche, Base, Codex, Ethereum, HyperEVM, Ink, Linea, OP Mainnet, Plume, Polygon PoS, Sei, Solana, Sonic, Unichain, World Chain, XDC <br /><br /> **Fast Transfer:** Arbitrum, Avalanche\*, Base, Codex, Ethereum, HyperEVM\*, Ink, Linea, OP Mainnet, Plume, Polygon PoS\*, Sei\*, Solana, Sonic\*, Unichain, World Chain, XDC\* <br /><br /> (\*) Destination chains only <br />                                                                                                          | **Standard Transfer:** Aptos, Arbitrum, Avalanche, Base, Ethereum, Noble, OP Mainnet, Polygon PoS, Solana, Sui, Unichain |
    | **Pricing**                | **Standard Transfer:** onchain [fee](/cctp/technical-guide#cctp-fees) (0) <br /><br /> **Fast Transfer:** onchain [fee](/cctp/technical-guide#cctp-fees) (per chain)                                                                                                                                                                                                                                                                                                                                                           | **Standard Transfer:** No fee                                                                                            |
    | **User Experience**        | Advanced cross-chain functionality, optimized for speed and composability                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Standard cross-chain functionality                                                                                       |
    | **Liquidity**              | Enables native USDC transfers post <Tooltip tip="The point at which a transaction is considered sufficiently secure for attestation, even though it has not yet reached hard finality. This allows for faster message processing while balancing the risk of chain reorganizations.">soft finality</Tooltip> and/or hard finality via a burn and mint method                                                                                                                                                                   | Enables native USDC transfers post hard finality via a burn and mint method                                              |
    | **Backward Compatibility** | Not backward compatible; forms a distinct network                                                                                                                                                                                                                                                                                                                                                                                                                                                                              | N/A                                                                                                                      |
  </Accordion>

  <Accordion title="Understanding the Problem">
    Blockchains often operate in siloed environments and cannot natively communicate
    with one another. While some ecosystems, such as Cosmos, use built-in protocols
    like the Inter-Blockchain Communication (IBC) protocol to enable data
    transmission between their appchains, direct communication between isolated
    networks, such as Ethereum and Avalanche, remains infeasible.

    Traditional bridges exist to address this limitation by enabling the transfer of
    digital assets, such as USDC, across blockchains. However, these bridges come
    with significant drawbacks. Two common methods, lock-and-mint bridging and
    liquidity pool bridging, require depositing USDC liquidity into third-party
    smart contracts. This approach reduces capital efficiency, acts as a target for
    malicious attacks, and introduces additional trust assumptions.
  </Accordion>

  <Accordion title="Design Approach">
    As a low-level primitive, CCTP can be embedded within any app, wallet, or bridge
    to enhance and simplify the user experience for crosschain use cases. With USDC
    circulating across a large number of blockchain networks, CCTP connects and
    unifies liquidity across the disparate ecosystems where it's supported.

    CCTP is built on generalized message passing and designed for composability and
    flexible use case enablement. Developers can extend its functionality beyond
    just moving USDC between blockchains. For example, you can create a flow where
    USDC is sent across chains and automatically deposited into a DeFi lending pool
    after the transfer, allowing it to generate yield in an automated manner. This
    experience can be designed to feel like a seamless, single transaction for the
    end user.
  </Accordion>
</AccordionGroup>

## How CCTP V2 works

CCTP V2 enables seamless and secure transfers of USDC across blockchains through
two transfer methods: **Fast Transfer** and **Standard Transfer**. Both involve
burning USDC on the source chain and minting it on the destination chain, but
the steps and speed differ:

<Tabs>
  <Tab title="Fast Transfer">
    **Fast Transfer** is an advanced feature of CCTP V2 designed for speed-sensitive
    use cases. It leverages Circle's Attestation Service and
    <Tooltip tip="Events are a logging mechanism used in smart contracts to emit information outside of the contract's storage variables. They are emitted, for example, when a token is transferred, allowing smart contracts to inform off-chain applications or users about state changes.">Fast Transfer Allowance</Tooltip> to enable *faster-than-finality*
    (soft finality) transfers. The process involves the following steps:

    1. **Initiation**. A user accesses an app powered by CCTP V2 and initiates a
       Fast Transfer of USDC, specifying the recipient's wallet address on the
       destination chain.
    2. **Burn Event**. The app facilitates a burn of the specified USDC amount on
       the source blockchain.
    3. **Instant Attestation**. Circle's Attestation Service attests to the burn
       event after soft finality (which varies per chain) and issues a signed
       attestation.
    4. **Fast Transfer Allowance Backing**. Until hard finality is reached, the
       burned USDC amount is backed by Circle's
       [Fast Transfer Allowance](/cctp/cctp-faq#what-is-the-fast-transfer-allowance-in-cctp-v2).
       The Fast Transfer Allowance is temporarily debited by the burn amount.
    5. **Mint event**. The app explicitly fetches the signed attestation from
       Circle's Attestation Service and uses it to mint USDC on the destination
       chain. A [fee](/cctp/technical-guide#cctp-fees) is collected onchain during
       this process.
    6. **Fast Transfer Allowance Replenishment**. Once the burn reaches finality on
       the source chain, the corresponding amount is credited back to Circle's Fast
       Transfer Allowance.
    7. **Completion**. The recipient wallet address receives the newly minted USDC
       on the destination blockchain, completing the transfer.

    **Fast Transfer** is ideal for low-latency use cases, enabling USDC transfers to
    be completed in seconds while maintaining trust and security via Circle's Fast
    Transfer Allowance.
  </Tab>

  <Tab title="Standard Transfer">
    **Standard Transfer** is the default method for transferring USDC across
    blockchains. It relies on transaction finality on the source chain and uses
    Circle's Attestation Service to enable standard-finality (hard finality)
    transfers. The process includes the following steps:

    1. **Initiation**. A user accesses an app powered by CCTP V2 and initiates a
       Standard Transfer of USDC, specifying the recipient's wallet address on the
       destination chain.
    2. **Burn Event**. The app facilitates a burn of the specified USDC amount on
       the source blockchain.
    3. **Attestation**. Circle's Attestation Service observes the burn event and,
       after observing hard finality on the source chain, issues a signed
       attestation. Hard finality ensures the burn is irreversible (about 15 to 19
       minutes for Ethereum and L2 chains.)
    4. **Mint Event**. The app explicitly fetches the signed attestation from
       Circle's Attestation Service and uses it to mint USDC on the destination
       chain. There might be a fee collected onchain during this step. For details,
       see
       [Standard Transfer Fee Switch](/cctp/technical-guide#standard-transfer-fee-switch).
    5. **Completion**. The recipient wallet address receives the newly minted USDC
       on the destination blockchain, completing the transfer.

    **Standard Transfer** is suitable for scenarios where longer finality times are
    acceptable.
  </Tab>
</Tabs>

<Note>
  **CCTP V2 White Paper**

  Read the
  [CCTP V2 White Paper](https://github.com/circlefin/evm-cctp-contracts/blob/master/whitepaper/CCTPV2_White_Paper.pdf)
  to learn about the motivation behind CCTP V2 and how the Fast Transfer
  Allowance balances speed, risk, and capital efficiency in crosschain USDC
  transfers.
</Note>

## Use Cases

CCTP enables developers to build novel crosschain apps that integrate
functionalities like trading, lending, payments, NFTs, and gaming, while
simplifying the user experience. Below are some practical examples of how you
can leverage CCTP in your applications—expand any to learn more.

<br />

<AccordionGroup>
  <Accordion title="Fast and secure crosschain rebalancing">
    Market makers, fillers/solvers, exchanges, and bridges can use CCTP to manage
    liquidity more efficiently. By securely rebalancing USDC holdings across
    blockchains, you can reduce operational costs, meet demand, and take advantage
    of market opportunities with minimal latency.
  </Accordion>

  <Accordion title="Composable crosschain swaps">
    With CCTP, users can quickly swap between digital assets on different
    blockchains by routing through USDC. Users can also swap for USDC and
    automatically trigger subsequent actions on the destination chain, seamlessly
    enabling complex crosschain actions such as swaps and deposits.
  </Accordion>

  <Accordion title="Programmable crosschain purchases">
    Automate crosschain purchases with CCTP. For example, a user can use USDC on one
    chain to purchase an NFT on a decentralized exchange on another chain and list
    it for sale on an NFT marketplace. When the transaction is initiated, CCTP
    routes USDC across chains to buy the NFT and opens the listing on the
    marketplace—all in one streamlined flow.
  </Accordion>

  <Accordion title="Simplify crosschain complexities">
    Simplify the crosschain experience by using USDC as collateral on one chain to
    open a borrowing position on a lending protocol on another chain. With CCTP,
    USDC can move quickly between blockchains, allowing users to onboard to new
    applications without switching wallets or managing multichain complexities.
  </Accordion>
</AccordionGroup>

<br />

**WHAT'S NEXT**

* [CCTP Technical Guide <Icon icon="arrow-right" />](/cctp/technical-guide)