> ## 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.
# Circle Gateway
Circle Gateway enables a unified USDC balance across multiple blockchains.
Deposit USDC to non-custodial Gateway Wallet contracts on any supported source
blockchain, then mint USDC instantly (\<500 ms) on any destination blockchain
using a single API call.
Gateway is fully permissionless, and you can start integrating with it
immediately with no sign-up needed. Check out the quickstart guides for
[EVM](/gateway/quickstarts/unified-balance-evm) and
[Solana](/gateway/quickstarts/unified-balance-solana).
**Use
[Unified Balance Kit](https://www.npmjs.com/package/@circle-fin/unified-balance-kit)
to simplify Gateway integrations.**
Unified Balance Kit handles deposit, transfer, and spend flows so you can build
Gateway-powered features in just a few lines of code.
## Key features
Hold USDC across multiple blockchains and access it as a single balance on
any supported destination blockchain
Transfer USDC in under 500 ms after your balance is established, with no
waiting for source blockchain finality
Retain full ownership of deposited USDC with signature-based authorization
and a 7-day trustless withdrawal option
Authorize transfers from smart contracts and smart contract wallets with
ERC-1271, without requiring a separate EOA delegate. See [ERC-1271
programmable authorization](/gateway/references/erc-1271).
## What you can build
Gateway enables applications that require instant access to USDC across
blockchains. Here are some common use cases:
Build applications where users interact with USDC without worrying about which
blockchain it's on. Users deposit once and access their balance instantly on any
supported blockchain.
Provide instant liquidity across blockchains without maintaining separate
balances on each chain. Consolidate USDC holdings and access them where needed.
Route payments to any supported blockchain instantly. Accept USDC on one
blockchain and settle on another without delays.
Reduce working capital requirements by consolidating USDC across blockchains
into a unified balance that's accessible anywhere.
Power AI agents and machine-to-machine systems with gasless, sub-cent USDC
payments through [Gateway Nanopayments](/gateway-nanopayments). See
[Agent Nanopayments](/agent-stack/agent-nanopayments) for the pre-built
agent-builder workflow.
## Get started
Build a script to deposit USDC on multiple blockchains and transfer it
instantly to a destination blockchain
Authorize Gateway transfers with ERC-1271 using a Circle SCA
Receive real-time notifications for Gateway events on your registered wallet
addresses
View the blockchains where you can deposit and mint USDC with Gateway
## Related products
CCTP and Gateway offer different approaches to crosschain transfers. This table
compares the two approaches.
| Attribute | CCTP | Gateway |
| - | - | - |
| **Use case** | Transfer USDC, EURC, or registered third-party assets from one blockchain to another | Hold a unified USDC balance accessible on any supported blockchain |
| **Transfer speed** | Fast Transfer: \~8-20 seconds
Standard Transfer: 15-19 minutes (Ethereum/L2s) | Instant (\<500 ms) after balance is established |
| **Balance model** | Point-to-point transfers | Unified crosschain balance |
| **Custody** | Non-custodial | Non-custodial with 7-day trustless withdrawal option |
| **Supported blockchains** | [View list](/cctp/concepts/supported-chains-and-domains) | [View list](/gateway/references/supported-blockchains) |