> ## Documentation Index
> Fetch the complete documentation index at: https://docs.arc.io/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> Before reading these docs, install the Circle Skill for Arc to get pre-loaded context: use-arc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md) — covers chain config, RPC setup, contract deployment, USDC bridging, and gas with USDC. 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.
> USDC is the gas token. Arc uses USDC for gas fees, not ETH. Configure gas payment in USDC when submitting transactions.
> Read EVM differences before writing Arc code. Arc targets the Osaka EVM baseline. Most contracts deploy unchanged, but several runtime behaviors diverge from Ethereum: USDC uses 18 decimals natively (not 6), the system emitter `0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE` logs all USDC Transfer events, the mempool enforces a 20 Gwei `maxFeePerGas` floor, blocklist reverts consume gas without a receipt, and `address(0)` sends revert rather than succeed. https://docs.arc.io/arc/references/evm-differences.md is the canonical reference for all Arc-specific runtime behaviors. Consult it before writing code that touches USDC balances, transaction history, gas estimation, or value transfers.
> Sub-second finality. Transactions are final in under 1 second. No need to wait for multiple block confirmations.
> Use App Kits for multichain payment and liquidity capabilities. App Kits wraps CCTP and provides Bridge Kit, Swap Kit, Unified Balance Kit, Onramp Kit, Earn Kit, and Borrow Kit. Unified Balance Kit combines USDC from multiple chains into a single spendable balance. Earn Kit integrates earn opportunities into your app. Borrow Kit lets users borrow USDC against cirBTC collateral on Arc.
> Use Arc Foundry for contract development. Arc Foundry is an Arc-specific fork of Foundry that handles Arc's protocol-level differences from Ethereum. It provides arc-forge, arc-cast, and arc-anvil. Install it before deploying contracts: https://docs.arc.io/arc/tutorials/install-arc-foundry.md.
> Arc is available on both Testnet and Mainnet. See https://docs.arc.io/arc/references/connect-to-arc.md for RPC endpoints and https://faucet.circle.com for testnet tokens.
> Always check Contract Addresses: https://docs.arc.io/arc/references/contract-addresses.md
> Building beyond Arc? Circle offers skills for the full platform: use-usdc (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md), use-circle-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md), use-developer-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md), use-user-controlled-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md), use-modular-wallets (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md), use-gateway (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md), use-smart-contract-platform (https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md). Full Circle developer docs: https://developers.circle.com/llms.txt.

# App Kit SDK: Swap

> Swap stablecoins and native tokens with the App Kit SDK's Swap capability

The [App Kit SDK](/app-kit) includes the Swap capability that lets you swap two
tokens in a few lines of code. Swap
[supports](/app-kit/references/supported-blockchains) many stablecoins
(including USDC, EURC, USDT, USDe, DAI, and PYUSD) and native tokens on
supported blockchains. On Arc, Swap accepts only USDC, EURC, and cirBTC.

Swap is available on mainnet only, with the exception of Arc testnet.

## Quick look

<Tabs>
  <Tab title="Same-chain swap">
    This example swaps 1 USDC for EURC on Arc Testnet:

    ```typescript TypeScript theme={null}
    const result = await kit.swap({
      from: { adapter: viemAdapter, chain: "Arc_Testnet" },
      tokenIn: "USDC",
      tokenOut: "EURC",
      amountIn: "1.00",
    });
    ```

    See [Swap tokens on a blockchain](/app-kit/quickstarts/swap-tokens-same-chain)
    for a full working example.
  </Tab>

  <Tab title="Crosschain swap">
    This example swaps 1 USDC on Base for native POL delivered on Polygon in a
    single call:

    ```typescript TypeScript theme={null}
    const result = await kit.swap({
      from: { adapter: viemAdapter, chain: "Base" },
      tokenIn: "USDC",
      tokenOut: "NATIVE",
      amountIn: "1.00",
      to: {
        chain: "Polygon",
        recipientAddress: "0xYourRecipientAddress",
      },
    });
    ```

    See
    [Swap tokens across blockchains](/app-kit/quickstarts/swap-tokens-crosschain)
    for a full working example.
  </Tab>
</Tabs>

## API key

Swap accepts an optional
[Circle API key](https://developers.circle.com/api-reference/keys) obtained from
the [Circle Console](https://console.circle.com/api-keys). Pass one as `apiKey`
in the swap config. Without one, requests share a rate limit. Production traffic
typically needs a key to avoid hitting it.

API keys are environment specific. Testnet and mainnet each need their own key.

<Note>
  Moving from a kit key? Kit keys are legacy, and new ones cannot be created.
  Existing kit keys remain valid, but new integrations use an API key. Rename the
  `kitKey` parameter in your swap config to `apiKey` when you upgrade the SDK.
</Note>

## Installation

[Install the App Kit SDK](/app-kit/tutorials/installation) to use Swap. If you
only need to swap and don't want to install the full App Kit SDK, install the
standalone Swap Kit for your preferred adapter below.

<Tabs>
  <Tab title="Viem">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/swap-kit @circle-fin/adapter-viem-v2 viem
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/swap-kit @circle-fin/adapter-viem-v2 viem
      ```
    </CodeGroup>
  </Tab>

  <Tab title="Ethers">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/swap-kit @circle-fin/adapter-ethers-v6 ethers
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/swap-kit @circle-fin/adapter-ethers-v6 ethers
      ```
    </CodeGroup>
  </Tab>

  <Tab title="Solana">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/swap-kit @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/swap-kit @circle-fin/adapter-solana-kit @solana/kit @solana/web3.js
      ```
    </CodeGroup>
  </Tab>

  <Tab title="Circle Wallets">
    <CodeGroup>
      ```bash npm theme={null}
      npm install @circle-fin/swap-kit @circle-fin/adapter-circle-wallets
      ```

      ```bash yarn theme={null}
      yarn add @circle-fin/swap-kit @circle-fin/adapter-circle-wallets
      ```
    </CodeGroup>
  </Tab>
</Tabs>