> ## 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.

# Supported blockchains and domains

> Blockchains, domains, and pre-configured tokens available on CCTP for non-USDC.

Non-USDC transfers are supported on EVM-compatible blockchains only. The domain
IDs are shared with CCTP. Trust is configured bilaterally: a domain must be
added as trusted on both ends before transfers can route between them.

## Supported blockchains

The following EVM-compatible blockchains have CCTP for non-USDC deployments. The
table includes both mainnet and testnet environments; domain IDs are consistent
across both. Non-EVM blockchains, including Solana, are not supported.

| Blockchain | Domain ID |
| - | - |
| Ethereum | 0 |
| Avalanche | 1 |
| OP Mainnet | 2 |
| Arbitrum | 3 |
| Base | 6 |
| Polygon PoS | 7 |
| Arc Testnet | 26 |

Domain IDs match the
[CCTP domain identifiers](/cctp/concepts/supported-chains-and-domains#domain-identifiers).
For deployed contract addresses, see
[Contract Addresses](/cctp/expanded-assets/references/contract-addresses).

## Pre-configured tokens

The following tokens are pre-configured on the supported blockchains. Token IDs
are stable identifiers used in API calls, contract interactions, and code
samples.

| Token | Symbol | Type | Token ID |
| - | - | - | - |
| Euro Coin | EURC | Custom | `0x6ca9e29fa53becc29becaf4a90b9ca7a995ad4d2234880da13ca38c657fb241c` |
| Circle Wrapped Bitcoin | cirBTC | Custom | `0x3d26699fb5d40190fc3fa0dcbc1cd24e558355043c1997572ff9fd6efbb3fdca` |
| Wrapped Ether | WETH | Ownerless | `0x5c2cf12eccf48ab63313169ce192dc00af7c37a58bbc546ba4becf54df4962ea` |

USDC transfers use standard CCTP. To transfer USDC across blockchains, use
[CCTP](/cctp).

To retrieve the full list of supported tokens and routes, including sandbox
token IDs and per-domain deployment addresses, query the Iris API. The endpoint
is paginated. Use `pageSize` to set the number of results per page, and
`pageAfter` with the `nextPageAfter` value from the previous response to advance
to the next page. Pass `tokenid` to filter by a specific token:

```bash theme={null}
# All tokens (mainnet)
curl https://iris-api.circle.com/v2/cctpx/tokens

# Filter by token ID (mainnet EURC)
curl "https://iris-api.circle.com/v2/cctpx/tokens?tokenid=0x6ca9e29fa53becc29becaf4a90b9ca7a995ad4d2234880da13ca38c657fb241c"

# All tokens (sandbox) with a custom page size
curl "https://iris-api-sandbox.circle.com/v2/cctpx/tokens?pageSize=150"

# Next page (sandbox)
curl "https://iris-api-sandbox.circle.com/v2/cctpx/tokens?pageSize=150&pageAfter=<nextPageAfter>"
```

## Domain trust

The `CrossChainTokenService` on each domain maintains its own list of trusted
remote domains. Both the source and destination services must list each other
before transfers route successfully. To check whether a remote domain is
configured on the local service, call
[`isTrustedDomain`](/cctp/expanded-assets/references/contract-reference).