> ## 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. # Release notes - Agent stack - 2026 > 2026 release notes for Agent Stack ## September 2026 ### Documentation additions Launched **Facilitator Service**, Circle's hosted [x402](/x402-facilitators/x402) facilitator for accepting USDC payments on Arc, Base, and Polygon PoS. * [Facilitator Service overview](/facilitator-service) * [How it works](/facilitator-service/how-it-works) * [Quickstart: Accept x402 payments](/facilitator-service/quickstart) * [Supported networks](/facilitator-service/supported-networks) * [API reference](/api-reference/facilitator-service/verify-payment) ### Blockchain expansion Added Arc mainnet as a supported blockchain for Agent Stack. Updated topics: * [Agent Nanopayments quickstart](/agent-stack/agent-nanopayments/quickstart) * [Deposit](/agent-stack/agent-nanopayments/operations/deposit) * [Pay for service](/agent-stack/agent-nanopayments/operations/pay-for-service) * [Withdraw](/agent-stack/agent-nanopayments/operations/withdraw) * [Agent Wallets quickstart](/agent-stack/agent-wallets/quickstart) * [Agent Wallets supported blockchains](/agent-stack/agent-wallets/supported-blockchains) * [Authenticate](/agent-stack/agent-wallets/wallet-operations/authenticate) * [Bridge](/agent-stack/agent-wallets/wallet-operations/bridge) * [Custom policies](/agent-stack/agent-wallets/wallet-operations/custom-policies) * [Execute contract](/agent-stack/agent-wallets/wallet-operations/execute-contract) * [Fund](/agent-stack/agent-wallets/wallet-operations/fund) * [Sign](/agent-stack/agent-wallets/wallet-operations/sign) * [Swap](/agent-stack/agent-wallets/wallet-operations/swap) * [Transfer](/agent-stack/agent-wallets/wallet-operations/transfer) * [Circle CLI command reference](/agent-stack/circle-cli/command-reference) ## August 2026 Released Circle CLI 1.0.0. This release includes the following user-facing changes: * Updated `circle gateway deposit --method eco` to use Eco's quoted, single-use deposit vaults. The command now waits for Eco to publish the deposit by default and supports `--no-wait` for asynchronous workflows. * Added version compatibility checks that guide you to `circle update` when a newer supported version is required. See the [CLI command reference](/agent-stack/circle-cli/command-reference) for complete command syntax, including the updated Eco deposit options. ## July 2026 Launched the **Agent Marketplace**, a curated catalog of [x402](/x402-facilitators/x402)-compatible services that accept USDC. Every listing is sanctions-screened and health-checked, so agents find services that are compliant and live. Two new integration paths: * **Buyers (AI agents)** discover services through the public, keyless [Discovery API](/agent-stack/agent-marketplace/discovery-api)—`GET https://api.circle.com/v2/x402/discovery/resources`—with 14 query parameters to filter by category, blockchain, price, and more. No API key or account required. * **Sellers (API owners)** list a service and get paid in USDC per call. See [Become a seller](/agent-stack/agent-marketplace/become-a-seller) for the nanopayments and vanilla x402 rails, or [Get listed](/agent-stack/agent-marketplace/get-listed) to submit a listing. Browse the live catalog at [agents.circle.com/services](https://agents.circle.com/services). ## May 2026 Added documentation for Agent Nanopayments, which enables AI agents to make sub-cent USDC payments to x402-compatible services using Circle CLI. ### Documentation additions The following Agent Nanopayments documentation was created: * [Agent nanopayments](/agent-stack/agent-nanopayments) * [Quickstart: Make a nanopayment](/agent-stack/agent-nanopayments/quickstart) * [Nanopayment operations](/agent-stack/agent-nanopayments/operations) * [How-to: Withdraw your balance](/agent-stack/agent-nanopayments/operations/withdraw) ### Documentation updates The following how-tos moved from Agent Wallets into the new Agent Nanopayments section: * [How-to: Deposit for nanopayments](/agent-stack/agent-nanopayments/operations/deposit) * [How-to: Pay for a service](/agent-stack/agent-nanopayments/operations/pay-for-service) Launched Agent Stack, a new product line for AI agents to manage wallets, transact onchain, and pay for x402-compatible services using Circle CLI. ### Documentation additions The following Agent Stack and Circle CLI documentation was created: * [Agent stack](/agent-stack) * [Circle CLI](/agent-stack/circle-cli) * [CLI command reference](/agent-stack/circle-cli/command-reference) The following Agent Wallets documentation was created: * [Agent wallets](/agent-stack/agent-wallets) * [Quickstart: Create an agent wallet](/agent-stack/agent-wallets/quickstart) * [Agent wallet supported blockchains](/agent-stack/agent-wallets/supported-blockchains) * [Agent wallet fees](/agent-stack/agent-wallets/fees) * [Wallet operations](/agent-stack/agent-wallets/wallet-operations) * [How-to: Authenticate an agent wallet](/agent-stack/agent-wallets/wallet-operations/authenticate) * [How-to: Fund an agent wallet](/agent-stack/agent-wallets/wallet-operations/fund) * [How-to: Transfer USDC](/agent-stack/agent-wallets/wallet-operations/transfer) * [How-to: Bridge USDC](/agent-stack/agent-wallets/wallet-operations/bridge) * [How-to: Swap tokens](/agent-stack/agent-wallets/wallet-operations/swap) * [How-to: Deposit for nanopayments](/agent-stack/agent-wallets/wallet-operations/nanopay) * [How-to: Pay for a service](/agent-stack/agent-wallets/wallet-operations/pay-for-service) * [How-to: Execute a smart contract](/agent-stack/agent-wallets/wallet-operations/execute-contract) * [How-to: Sign a message](/agent-stack/agent-wallets/wallet-operations/sign) * [How-to: Set spending policies](/agent-stack/agent-wallets/wallet-operations/custom-policies)