> ## 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.

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# Cross-Chain Transfer Protocol V1

> Move USDC securely across blockchains and simplify user experience

<Warning>
  **This is CCTP V1 (Legacy) version. For the latest version, see [CCTP](/cctp)**.
</Warning>

## Overview

**Cross-Chain Transfer Protocol V1** is a permissionless onchain utility that
facilitates USDC transfers securely between blockchain networks via native
burning and minting. Circle created CCTP to improve capital efficiency and
minimize trust requirements when using USDC across blockchain networks. CCTP V1
enables developers to build multichain applications that allow users to perform
1:1 transfers of USDC securely across blockchains.

<Note>
  **Note:** CCTP V1 only supports **Standard Transfer**, constrained by
  blockchain finality on the source blockchain. Later [CCTP](/cctp) versions
  support **Fast Transfer** and **Hooks**, in addition to also supporting
  **Standard Transfer**.
</Note>

## Understanding the Problem

Blockchain networks 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 locking USDC liquidity in third-party smart
contracts. This approach reduces capital efficiency and introduces additional
trust assumptions.

## Design Approach

As a low-level primitive, CCTP V1 can be embedded within any app or wallet -
even existing bridges - to enhance and simplify the user experience for
cross-chain use cases. With USDC circulating across a large number of blockchain
networks, CCTP V1 can connect and unify liquidity across disparate ecosystems
where it's supported.

CCTP V1 is built on generalized message passing and designed for composability,
enabling a wide range of use cases. 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.

## How CCTP V1 works

**Standard Transfer** is the default method in CCTP V1 for transferring USDC
across blockchains, which involves burning USDC on the source chain and minting
it on the destination chain. It relies on transaction finality on the source
chain and uses Circle's Attestation Service to enable standard-finality
(<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>) transfers. The process includes the following steps:

1. **Initiation**. A user accesses an app powered by CCTP V1 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 13 to 19
   minutes for Ethereum and L2 chains.)
4. **Mint Event**. The app retrieves the signed attestation from Circle and uses
   it to mint USDC on the destination chain.
5. **Completion**. The recipient wallet address receives the newly minted USDC
   on the destination blockchain, completing the transfer.

**Standard Transfer** prioritizes reliability and security, making it suitable
for scenarios where finality wait times are acceptable.

## Use Cases

CCTP V1 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 V1 in your applications, either directly or indirectly by
routing USDC behind the scenes:

### Cross-chain rebalancing

Market makers, fillers/solvers, exchanges, and bridges can use CCTP V1 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.

### Cross-chain swaps

With CCTP V1, 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, enabling
seamless cross-chain transactions.

### Cross-chain purchases

Automate cross-chain purchases with CCTP V1. 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
V1 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 V1,
USDC can move quickly between blockchains, allowing users to onboard to new
applications without switching wallets or managing multi-chain complexities.