> ## 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. # xReserve supported blockchains and domains ## Supported blockchains xReserve operates across multiple blockchains. Each supported blockchain serves one or more of the following roles: * **Source chains** where Circle-deployed xReserve smart contracts hold [USDC reserves](/xreserve/concepts/technical-guide#usdc-reserve). * **Remote chains** where USDC-backed stablecoins are issued. * **Destination chains** where USDC or USDC-backed stablecoins are ultimately withdrawn. ### Source chains The following tables list the mainnet and testnet blockchains where xReserve smart contracts have been deployed. Users deposit USDC into these contracts to receive an equal amount of USDC-backed stablecoins on remote blockchains. **Mainnet** | Blockchain | USDC token address | xReserve contract address | | - | - | - | | Arc | [`0x3600000000000000000000000000000000000000`](https://explorer.arc.io/token/0x3600000000000000000000000000000000000000) | [`0x8888888199b2Df864bf678259607d6D5EBb4e3Ce`](https://explorer.arc.io/address/0x8888888199b2Df864bf678259607d6D5EBb4e3Ce) | | Ethereum | [`0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48`](https://etherscan.io/token/0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48) | [`0x8888888199b2Df864bf678259607d6D5EBb4e3Ce`](https://etherscan.io/address/0x8888888199b2Df864bf678259607d6D5EBb4e3Ce) | **Testnet** | Blockchain | USDC token address | xReserve contract address | | - | - | - | | Arc Testnet | [`0x3600000000000000000000000000000000000000`](https://explorer.testnet.arc.io/token/0x3600000000000000000000000000000000000000) | [0x008888878f94C0d87defdf0B07f46B93C1934442](https://explorer.testnet.arc.io/address/0x008888878f94C0d87defdf0B07f46B93C1934442) | | Ethereum Sepolia | [`0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238`](https://sepolia.etherscan.io/token/0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238) | [0x008888878f94C0d87defdf0B07f46B93C1934442](https://sepolia.etherscan.io/address/0x008888878f94C0d87defdf0B07f46B93C1934442) | ### Remote chains The following tables list the mainnet and testnet xReserve partner blockchains where USDC-backed stablecoins can be minted. **Mainnet** | Blockchain | Token symbol | Token address or identifier | | - | - | - | | Aleo | USDCx | [`usdcx_stablecoin.aleo`](https://explorer.provable.com/program/usdcx_stablecoin.aleo) | | Canton | USDCx | `InstrumentId.id`: `USDCx`
`InstrumentId.admin`: [`decentralized-usdc-interchain-rep::12208115f1e168dd7e792320be9c4ca720c751a02a3053c7606e1c1cd3dad9bf60ef`](https://api.utilities.digitalasset.com/api/token-standard/v0/registrars/decentralized-usdc-interchain-rep::12208115f1e168dd7e792320be9c4ca720c751a02a3053c7606e1c1cd3dad9bf60ef/registry/metadata/v1/instruments) | | Cardano | USDCx | [`1f3aec8bfe7ea4fe14c5f121e2a92e301afe414147860d557cac7e345553444378`](https://cardanoscan.io/token/1f3aec8bfe7ea4fe14c5f121e2a92e301afe414147860d557cac7e345553444378) | | Movement | USDCx | [`0xba11833544a2f99eec743f41a228ca6ffa7f13c3b6b04681d5a79a8b75ff225e`](https://explorer.movementnetwork.xyz/fa/0xba11833544a2f99eec743f41a228ca6ffa7f13c3b6b04681d5a79a8b75ff225e?network=mainnet) | | Stacks | USDCx | [`SP120SBRBQJ00MCWS7TM5R8WJNTTKD5K0HFRC2CNE.usdcx`](https://explorer.hiro.so/txid/SP120SBRBQJ00MCWS7TM5R8WJNTTKD5K0HFRC2CNE.usdcx?chain=mainnet) | **Testnet** | Blockchain | Token symbol | Token address or identifier | | - | - | - | | Aleo Testnet | USDCx | [`test_usdcx_stablecoin.aleo`](https://testnet.explorer.provable.com/program/test_usdcx_stablecoin.aleo) | | Canton TestNet | USDCx | `InstrumentId.id`: `USDCx`
`InstrumentId.admin`: [`decentralized-usdc-interchain-rep::122049e2af8a725bd19759320fc83c638e7718973eac189d8f201309c512d1ffec61`](https://api.utilities.digitalasset-staging.com/api/token-standard/v0/registrars/decentralized-usdc-interchain-rep::122049e2af8a725bd19759320fc83c638e7718973eac189d8f201309c512d1ffec61/registry/metadata/v1/instruments) | | Cardano Preprod | USDCx | [`31dde3db98ad05feb688d4dbb146b3b6054e1246cbcef98c79b0bf665553444378`](https://preprod.cardanoscan.io/token/31dde3db98ad05feb688d4dbb146b3b6054e1246cbcef98c79b0bf665553444378) | | Movement Bardock | USDCx | [`0xa9bb719984ec9c61d6cd4542f3efaaa01caf9d2ab85e8f7c9e4abcd304573f87`](https://explorer.movementnetwork.xyz/fa/0xa9bb719984ec9c61d6cd4542f3efaaa01caf9d2ab85e8f7c9e4abcd304573f87?network=testnet) | | Stacks Testnet | USDCx | [`ST2WK9SGBJ15RHZ33KK0KYVSXBEBHM1XDM8C96EC4.usdcx`](https://explorer.hiro.so/txid/ST2WK9SGBJ15RHZ33KK0KYVSXBEBHM1XDM8C96EC4.usdcx?chain=testnet) | ### Destination chains These are the destination blockchains where USDC or USDC-backed stablecoins are ultimately withdrawn: * [Gateway supported blockchains](/gateway/references/supported-blockchains): Because xReserve holds USDC in Gateway wallets, users can withdraw USDC on any Gateway supported blockchain, including the source chain. * [CCTP supported blockchains](/cctp/cctp-supported-blockchains): If a blockchain is not supported by Gateway, xReserve uses CCTP to forward the funds to another blockchain. This lets users withdraw USDC on any CCTP supported blockchain. * Another [remote blockchain](#remote-chains): Users can burn USDC-backed stablecoins on one remote blockchain to withdraw USDC-backed stablecoins on a different remote blockchain. ## Domain identifiers A domain is a Circle-issued numeric identifier for a blockchain. xReserve uses domain identifiers in messages and attestations. Domain identifiers don't map to any existing public chain ID. xReserve domains fall into two categories: * **Source domains** are the blockchains on which USDC is held in an xReserve contract. * **Remote domains** are the blockchains on which USDC-backed stablecoins are deployed, minted, and circulated. Use the [Get domain information](/api-reference/xreserve/all/get-info) endpoint to retrieve a list of all source and remote domains. ### Source domains | Domain | Name | | - | - | | 0 | Ethereum | | 26 | Arc | ### Remote domains | Domain | Name | | - | - | | 10001 | Canton | | 10002 | Aleo | | 10003 | Stacks | | 10004 | Cardano | | 10005 | Movement |