> ## 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. # Exchange Integration > Integrate Arc deposits, withdrawals, and USDC liquidity management into your exchange. Arc is an EVM-compatible Layer 1 blockchain where USDC is the native gas token. For exchanges, this means simpler hot wallet operations, instant settlement finality, and a single asset to manage for both trading and transaction fees. ## Key differences for exchanges Three Arc design decisions affect every exchange integration: | Concern | Arc behavior | Impact on exchanges | | :- | :- | :- | | **Deterministic finality** | Transactions finalize in under 1 second with no reorgs | Credit deposits after a single confirmation. No multi-block wait required. | | **USDC as gas** | Transaction fees are paid in USDC | No separate gas token funding for hot wallets. One asset covers fees and transfers. | | **Dual USDC interface** | Native balance (18 decimals) and ERC-20 interface (6 decimals) share the same underlying balance | One USDC balance underlies both interfaces. `eth_getBalance` and system emitter events cover all deposit activity. | ## Operational areas Exchange integration covers three workflows: * **Deposits**—Subscribe to new blocks and detect incoming USDC transfers. Deterministic finality means a single confirmation is final. * **Withdrawals**—Build, sign, and broadcast USDC transfers from your hot wallet. Gas is paid in USDC from the same balance. * **Liquidity (CCTP bridging)**—Move USDC between Arc and other blockchains using Cross-Chain Transfer Protocol to manage treasury and liquidity pools. ## Arc behaviors relevant to this integration The following Arc behaviors can affect exchange operations. Each is covered in [EVM differences](/arc/references/evm-differences): * **Filter deposit events on the system emitter, not the ERC-20 contract address:** Every native USDC movement emits a `Transfer` log from the system emitter (`0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE`). Plain native sends emit no log at the ERC-20 contract address (`0x3600000000000000000000000000000000000000`); filtering that address alone silently misses them. An ERC-20 `transfer()` emits logs at both addresses; count only the system emitter to avoid double-crediting. System emitter log values are in 18-decimal precision. See [Detect deposits](/integrate/exchanges/deposits). * **`balanceOf` zero does not mean no USDC:** `balanceOf()` returns 0 for amounts under 1×10⁻⁶ USDC (6-decimal minimum). Accounts hold sub-minimum dust spendable as gas. See [USDC as the native gas token](/arc/references/evm-differences#usdc-as-the-native-gas-token). * **Blocklist enforcement:** Transfers to or from a blocklisted address revert at runtime. The transaction is included in the block and consumes gas, but state changes roll back. Check the destination address against `isBlacklisted()` on the USDC contract before submitting withdrawals. See [Process withdrawals](/integrate/exchanges/withdrawals#step-2-check-the-blocklist). * **Deposit attribution in EIP-3009 relayer flows:** For deposits submitted by an EIP-3009 (`transferWithAuthorization`) relayer, attributing from `tx.from` credits the relayer's address, not the depositor's. Use the `from` field in the system emitter's `Transfer` event for accurate attribution. See [Detect deposits](/integrate/exchanges/deposits). * **Block timestamps are non-decreasing, not strictly increasing:** Sub-second blocks can share the same timestamp. Use block number, not `block.timestamp`, for deposit sequencing and event ordering. See [Fee market and block behavior](/arc/references/evm-differences#fee-market-and-block-behavior). * **Minimum base fee is 20 Gwei:** Transactions with `maxFeePerGas` under 20 Gwei are rejected by the mempool. This applies to all hot wallet operations, including withdrawals and deposit sweeps. See [Process withdrawals](/integrate/exchanges/withdrawals#step-5-build-the-eip-1559-transaction). * **Transaction attribution with Memo contracts:** For transfers routed through the Memo contract (`0x5294E9927c3306DcBaDb03fe70b92e01cCede505`) or Multicall3From (`0x522fAf9A91c41c443c66765030741e4AaCe147D0`), the CallFrom precompile preserves the original sender, so `tx.from` and the `Transfer` event's `from` are still your EOA wallet. For compliance attribution, read from the `Transfer` logs and the `Memo` event's indexed `sender`. See [Process withdrawals](/integrate/exchanges/withdrawals#attach-memos-for-compliance). ## What you need Before you start, confirm you have the following: | Requirement | Details | | :- | :- | | RPC access | `https://rpc.testnet.arc.io` (HTTPS) or `wss://rpc.testnet.arc.io` (WebSocket) | | Chain ID | `5042002` (testnet) | | USDC ERC-20 contract | [`0x3600000000000000000000000000000000000000`](https://explorer.testnet.arc.io/address/0x3600000000000000000000000000000000000000) | | CCTP contracts (for bridging) | TokenMessengerV2: [`0x8FE6B999Dc680CcFDD5Bf7EB0974218be2542DAA`](https://explorer.testnet.arc.io/address/0x8FE6B999Dc680CcFDD5Bf7EB0974218be2542DAA), Domain: `26` | | Memo contract (compliance metadata) | [`0x5294E9927c3306DcBaDb03fe70b92e01cCede505`](https://explorer.testnet.arc.io/address/0x5294E9927c3306DcBaDb03fe70b92e01cCede505) | | Custody provider supporting custom EVM | See [Add custody platform support](/integrate/exchanges/custody) for configured providers and setup steps | ## Integration guides Subscribe to blocks and detect incoming USDC transfers with single-confirmation finality. Build, sign, and broadcast withdrawal transactions using USDC for both value and gas. Move USDC liquidity to and from Arc using Cross-Chain Transfer Protocol. Register Arc in supported custody platforms.