> ## 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 - Bridge Kit - 2026

> 2026 release notes for Circle's Bridge Kit SDK

<Check>
  **Bridge Kit has [moved to Arc](https://docs.arc.io/app-kit/bridge).**
</Check>

## March 2026

<Update label="2026.03.17">
  Bridge Kit is now part of [Arc App Kits](https://docs.arc.io/app-kit/).

  ### Documentation updates

  Migrated Bridge Kit documentation to the Arc developer docs:

  * [App Kit SDK: Bridge](https://docs.arc.io/app-kit/bridge)
</Update>

<Update label="2026.03.10">
  Bridge Kit now supports Morph mainnet and Morph Hoodi Testnet (CCTP).

  ### Documentation updates

  Updated the following documentation to reflect support for Morph:

  * [Supported Blockchains](https://docs.arc.io/app-kit/references/supported-blockchains)
</Update>

<Update label="2026.03.09">
  Bridge Kit now supports EDGE mainnet and EDGE Testnet (CCTP).

  ### Documentation updates

  Updated the following documentation to reflect support for EDGE:

  * [Supported Blockchains](https://docs.arc.io/app-kit/references/supported-blockchains)
</Update>

## February 2026

<Update label="2026.02.27">
  Bridge Kit now supports the Circle Forwarding Service.

  ### Documentation additions

  Added the following documentation to reflect support for the Forwarding Service:

  * [Use the Forwarding Service](https://docs.arc.io/app-kit/tutorials/bridge/use-forwarding-service)

  ### Documentation updates

  Updated the following documentation to include the Forwarding Service fee:

  * [Custom Fees](https://docs.arc.io/app-kit/concepts/bridge-fees)
</Update>

## January 2026

<Update label="2026.01.28">
  Bridge Kit now supports Monad.

  ### Documentation updates

  Updated the following documentation to reflect support for Monad mainnet and
  testnet:

  * [Supported Blockchains](https://docs.arc.io/app-kit/references/supported-blockchains)
</Update>

<Update label="2026.01.14">
  The `estimate()` function now returns `token`, `amount`, `source`, and
  `destination` fields alongside cost estimates. Exported error type guards (such
  as `isKitError`, `isBalanceError`, `isOnchainError`), error constants (such as
  `BalanceError`, `OnchainError`), and helper functions (`getErrorCode`,
  `getErrorMessage`) for improved error detection and recovery.

  ### Documentation updates

  Updated the following documentation to reflect new method names and features:

  * [Bridge Kit Installation](https://docs.arc.io/app-kit/tutorials/installation)
  * [Quickstart: Bridge USDC Between EVM Chains](https://docs.arc.io/app-kit/quickstarts/bridge-between-evm-chains)
  * [Quickstart: Bridge USDC between Solana and EVM](https://docs.arc.io/app-kit/quickstarts/bridge-between-solana-and-evm)
  * [Adapter Setups](https://docs.arc.io/app-kit/tutorials/adapter-setups)
  * [Collect a Transfer Fee](https://docs.arc.io/app-kit/tutorials/bridge/collect-bridge-fee)
  * [Estimate Costs Before Transferring](https://docs.arc.io/app-kit/tutorials/bridge/estimate-costs)
  * [Configure Transfer Speed and Maximum Cost](https://docs.arc.io/app-kit/tutorials/bridge/configure-transfer-speed)
  * [Specify Recipient Address](https://docs.arc.io/app-kit/tutorials/bridge/specify-recipient-address)
  * [Error Recovery and Troubleshooting](https://docs.arc.io/app-kit/references/bridge-error-recovery)
  * [Bridge Kit SDK Reference](https://docs.arc.io/app-kit/references/sdk-reference)
</Update>