> ## 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. # Upfront fee quotes > Request a signed quote for CCTP Fast Transfer and Forwarding Service fees and learn how fee types and quote expiry work. A fee quote is a signed, [time-bound](#quote-expiry) price for the upfront fees on a specific transfer. Requesting one locks in the Fast Transfer fee, the Forwarding Service fee, or both, so you know the exact cost before you submit the transfer. To see where the quote fits in the end-to-end flow, see [How upfront fees work](/cctp/concepts/how-upfront-fees-work). ## Requesting a quote Call [`POST /v2/quote/burn/usdc/{sourceDomainId}/{destDomainId}`](/api-reference/cctp/all/create-usdc-burn-quote) with these request fields: * `amount`: the USDC transfer amount, in minor units. * `feeToken`: the token you want to pay fees in. Use the zero address (the default) to price the fee in the native gas token, or the source blockchain's USDC address to price it in USDC. * `requests`: the fees to price. Include a `FORWARD` request for the Forwarding Service fee, a `PRE_FINALITY` request for the Fast Transfer fee, or both, with at most one of each type. The response includes the `signedQuote` blob you submit onchain, the total fee and fee token, a per-type breakdown, and the quote's issue time and expiry. A quote is bound to the exact transfer it prices. Request the quote with the same amount and destination domain you submit onchain. For a `FORWARD` fee, also match the destination caller and hook data. If any bound value differs when you submit, the transfer reverts. ## Fee types You can pay two types of fees upfront, one per service. | Fee type | Service | | - | - | | `FORWARD` | [Forwarding Service](/cctp/concepts/forwarding-service) | | `PRE_FINALITY` | [Fast Transfer](/cctp/concepts/fees) | A `FORWARD` request requires a destination domain where Forwarding Service is supported, and a `PRE_FINALITY` request requires a source blockchain available for Fast Transfers. See [Supported blockchains](/cctp/concepts/supported-chains-and-domains) for the blockchains that support each service. ## Quote expiry Each quote expires after a short, fixed window that depends on the source blockchain. Submit the transfer before the quote expires; otherwise, request a new quote. The following table lists the approximate expiry window for each supported source blockchain. These values are subject to change. | Source blockchain | Approximate quote expiry | | - | - | | Arbitrum | 2 minutes | | Arc testnet | 2 minutes | | Avalanche | 2 minutes | | Base | 2 minutes | | Codex | 2 minutes | | Ethereum | 2 minutes 30 seconds | | HyperEVM | 2 minutes | | Ink | 2 minutes | | Linea | 2 minutes | | Monad | 2 minutes | | OP Mainnet | 2 minutes | | Plume | 2 minutes | | Polygon PoS | 2 minutes | | Sei | 2 minutes | | Sonic | 2 minutes | | Unichain | 2 minutes | | World Chain | 2 minutes | | XDC | 2 minutes | A quote's expiry is either an exact wall-clock time or a source blockchain block number. For a block-number expiry, translating it into remaining time requires knowing the source blockchain and its live block height.