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.
Cross-Chain Transfer Protocol (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.
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 cross-chain composability by allowing you to trigger automated actions post-transfer. For more details, see the Hooks section.
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.
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 Standard Transfer: hard finality, ~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, Linea, OP Mainnet, Polygon PoS, Sei, Solana, Sonic, Unichain, World Chain Fast Transfer: Arbitrum, Avalanche*, Base, Codex, Ethereum, Linea, OP Mainnet, Polygon PoS*, Sei*, Solana, Sonic*, Unichain, World Chain (*) Destination chains only | Standard Transfer: Aptos, Arbitrum, Avalanche, Base, Ethereum, Noble, OP Mainnet, Polygon PoS, Solana, Sui, Unichain |
| Pricing | Standard Transfer: onchain fee (0) Fast Transfer: onchain fee (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 soft finality and/or hard finality via a burn and mint method | Enables native USDC transfers post via a burn and mint method |
| Backward Compatibility | Not backward compatible; forms a distinct network | N/A |
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.
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 cross-chain 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.
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:
- Fast Transfer
- Standard Transfer
Fast Transfer is an advanced feature of CCTP V2 designed for speed-sensitive use cases. It leverages Circle's Attestation Service and Fast Transfer Allowance to enable faster-than-finality (soft finality) transfers. The process involves the following steps:
- 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.
- Burn Event. The app facilitates a burn of the specified USDC amount on the source blockchain.
- Instant Attestation. Circle's Attestation Service attests to the burn event after soft finality (which varies per chain) and issues a signed attestation.
- Fast Transfer Allowance Backing. Until hard finality is reached, the burned USDC amount is backed by Circle's Fast Transfer Allowance. The Fast Transfer Allowance is temporarily debited by the burn amount.
- 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 is collected onchain during this process.
- 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.
- 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.
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:
- 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.
- Burn Event. The app facilitates a burn of the specified USDC amount on the source blockchain.
- 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.)
- 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.
- 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.
CCTP V2 White Paper
Read the CCTP V2 White Paper to learn about the motivation behind CCTP V2 and how the Fast Transfer Allowance balances speed, risk, and capital efficiency in cross-chain USDC transfers.
CCTP enables developers to build novel cross-chain 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.
Fast and secure cross-chain 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.
Composable cross-chain 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 cross-chain actions such as swaps and deposits.
Programmable cross-chain purchases
Automate cross-chain 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.
Simplify cross-chain complexities
Simplify the cross-chain 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 multi-chain complexities.
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