> ## 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.

# Stablecoin FX

> Build real-time, onchain stablecoin FX products with transparent pricing, instant settlement, and predictable fees on Arc.

Build onchain stablecoin FX and swap products on Arc. With native multi-currency
support, [sub-second settlement](/arc/concepts/deterministic-finality), and
composable crosschain liquidity with [App Kits](/app-kit), Arc gives you the
infrastructure for transparent, low-cost currency exchange.

For direct wallet-to-wallet transfers, see [P2P Payments](/build/payments). For
merchant checkout flows, see [eCommerce Checkout](/build/ecommerce).

## Sample apps

Production-ready examples on GitHub you can fork and customize.

<Columns cols={3}>
  <Card title="Arc stablecoin FX" icon="arrows-rotate" href="https://github.com/circlefin/arc-stablecoin-fx">
    Real-time USDC and EURC swaps with configurable platform fee collection
    using App Kit, developer-controlled wallets, and Supabase.
  </Card>

  <Card title="Arc fintech" icon="building-columns" href="https://github.com/circlefin/arc-fintech">
    Multichain treasury system with crosschain capital movement using Circle
    Developer-Controlled Wallets, Gateway, and Bridge Kit.
  </Card>

  <Card title="Arc multichain wallet" icon="wallet" href="https://github.com/circlefin/arc-multichain-wallet">
    Unified USDC balance and crosschain transfers using Circle Gateway, Next.js,
    and Supabase.
  </Card>
</Columns>

## Quickstarts

Get up and running with FX and swap flows in minutes.

<Columns cols={2}>
  <Card title="Swap tokens" icon="arrows-rotate" href="/app-kit/quickstarts/swap-tokens-same-chain">
    **Beginner**. Exchange one token for another on the same blockchain using
    the [Swap](/app-kit/swap) capability.
  </Card>

  <Card title="Swap tokens crosschain" icon="globe" href="/app-kit/quickstarts/swap-tokens-crosschain">
    **Intermediate**. Combine [bridging](/app-kit/bridge) and
    [swapping](/app-kit/swap) to exchange tokens across blockchains.
  </Card>

  <Card title="Bridge tokens across blockchains" icon="bridge" href="/app-kit/quickstarts/bridge-tokens-across-blockchains">
    **Beginner**. Transfer USDC between blockchains using [App
    Kit](/app-kit/bridge).
  </Card>

  <Card title="Deposit and spend a Unified Balance" icon="coins" href="/app-kit/quickstarts/unified-balance-deposit-and-spend">
    **Intermediate**. Combine USDC from multiple blockchains into a single,
    instantly spendable balance.
  </Card>
</Columns>

## Why Arc for stablecoin FX

Arc is purpose-built for stablecoin finance. These capabilities directly support
FX and swap applications.

<AccordionGroup>
  <Accordion title="Real-time settlement">
    [Deterministic finality](/arc/concepts/deterministic-finality)—the guarantee
    that a confirmed transaction cannot be reversed or reorganized—settles FX
    trades in under a second, giving counterparties immediate certainty.
  </Accordion>

  <Accordion title="Transparent pricing">
    Onchain swap rates with configurable slippage tolerance give users full
    visibility into execution price. See [set slippage
    tolerance](/app-kit/tutorials/swap/set-slippage-tolerance-or-stop-limit).
  </Accordion>

  <Accordion title="Multi-stablecoin pairs">
    Swap between USDC, EURC, and other supported stablecoins natively on Arc.
    See [contract addresses](/arc/references/contract-addresses) for available
    tokens and [swap fees](/app-kit/concepts/swap-fees) for pricing details.
  </Accordion>

  <Accordion title="Predictable fees">
    Stable USDC-denominated [gas fees](/arc/references/gas-and-fees) remove fee
    volatility from FX calculations, so you can quote accurate rates.
  </Accordion>

  <Accordion title="Crosschain liquidity">
    App Kits [bridges](/app-kit/bridge) and [swaps](/app-kit/swap) compose
    across chains for multi-leg FX routing without custom infrastructure.
  </Accordion>

  <Accordion title="Fee monetization">
    Collect a custom spread fee on every swap without writing new smart
    contracts. See [collect swap fee](/app-kit/tutorials/swap/collect-swap-fee).
  </Accordion>
</AccordionGroup>