Read the docs. Then ask the chain.

Network facts

The decimal trap

This is the single most dangerous thing about building on Arc.

Native USDC and the ERC-20 USDC interface are one balance with two views:

Verified on chain: decimals() → 6, symbol() → USDC.

• USDC.balanceOf(a) and a.balance describe the same money at different scales. Mixing them raw is a 10¹² error.
• The 6-decimal view truncates. A native balance of 0.0000001 USDC reads as 0 — so balanceOf(x) == 0 does not mean the account is empty.
• No WETH-style wrapper is needed: native USDC already satisfies IERC20.
• Solidity's ether unit is just 1e18, which on Arc means 1 USDC.

Protocol divergences from Ethereum

Compared against Ethereum at the Osaka hard fork, Arc's baseline.

Two event streams for one movement

Both emitters use topic0 0xddf252ad…3b3ef, so filtering by topic alone picks up both. Measured over 150 recent blocks: 1,589 native logs and 1,073 ERC-20 logs for 1,589 real movements.

Rules the native emitter follows, all confirmed on chain:

• The native log is emitted first, before other logs in the transaction.
• Zero-value transfers emit no log.
• Self-transfers (from == to) emit no log — but the ERC-20 contract still emits one, per the token standard. Seven appeared in a 150-block window.
• Mint is Transfer(0x0, to, v); burn is Transfer(from, 0x0, v).
• Gas fees are not logged, so replaying logs under-counts a fee payer's outflow. That residual is the expected signature of a correct index.

Before the Zero5 hard fork, testnet emitted NativeCoin* events from 0x1800…0000 instead. Backfills crossing that boundary need both shapes.

Contract addresses

Arc Testnet. All verified deployed.

Multicall3From is Arc-specific: it batches like Multicall3 but preserves the original msg.sender in each subcall. Memo and Multicall3From must be in the call path for Circle's compliance screening to see the memo.

Gaps found in Arc's documentation

These surfaced while building against the chain, and are worth contributing back:

1. The eth_getLogs range caps are undocumented, differ across the four endpoints the docs present as interchangeable, and the default endpoint's error message quotes a limit more than 3× what it enforces.
2. Cloudflare rate limiting on the public RPC is not mentioned.
3. The ERC-8004 registry read ABI is absent — the tutorials cover writes only.
4. readFeedback's return tuple has no published layout.
5. AgentIdentity has no totalSupply(), and nothing documents how to enumerate.

Sources

• docs.arc.io/llms.txt — full documentation index
• EVM differences
• USDC system events
• Gas and fees
• Contract addresses
• Agentic economy