클래식 x402에서는 구매자와 판매자 사이에 퍼실리테이터가 있습니다. Arc에서는 이를 생략했습니다 — 에이전트가 EIP-3009 서명 후 스스로 트랜잭션을 전송하는 self-settle 방식입니다. 가스비도 USDC라서 하나의 자산으로 결제와 수수료를 모두 처리합니다.
In classic x402, a facilitator sits between the buyer and the seller: it takes the agent's signature and broadcasts the transaction on its behalf. Convenient — but an extra party to trust, an extra API to wait on, an extra point of failure.
On Arc we skipped it. The scheme is called self-settle — "settle it yourself".
The agent receives the 402 invoice, signs an EIP-3009 authorization (exactly 5 USDC to the treasury) and broadcasts on Arc itself — gas is paid in USDC. The server reads the receipt from the block: the Transfer event reached the treasury — access opens for 30 days.
Why Arc makes this possible
Arc is a blockchain built by Circle — the company behind USDC. Its signature feature: gas is paid in USDC, not in a separate token. A conventional agent would need to hold two assets: USDC for the payment and ETH for gas. On Arc one balance is enough — USDC covers both the payment and the fee.
For the tokenized-stocks market this closes the loop: bStocks settle in USDC on Binance, the agent's gas is USDC, and the data subscription is USDC. One asset for trading, for fees, and for information — that is what a market built for machines looks like.
The flow in 6 steps
- The agent requests data → gets a 402 with the invoice: scheme, network, amount, recipient.
- It signs an EIP-3009 authorization — the standard for "transfer with authorization": a signature that permits moving exactly 5 USDC from the agent's wallet to the recipient. Nothing more, no wallet access.
- It broadcasts the transaction itself (hence "client-broadcast").
- It waits for confirmation — seconds.
- It retries the request with the transaction hash attached.
- The server reads the blockchain: is the tx in a block, did USDC reach the treasury, is the amount right → access for 30 days.
What the server actually verifies
Not a signature — a receipt. The server asks the chain for getTransactionReceipt(txHash) and checks: the transaction is really in a block, it contains a Transfer event from the USDC contract to the treasury address, the amount covers the price. This cannot be forged: either the transaction is in a block or it does not exist.
What this gives the ecosystem
Removing the facilitator removes a point of failure and a trust assumption. Any wallet holding USDC on Arc becomes a payment client: one asset, one signature, one RPC call. For agents, buying data becomes as routine as calling an API.
This is infrastructure for the tokenized-assets ecosystem, not a demo. Real-time delta data is what keeps bStock prices honest — and the agents that buy it settle on Arc in USDC, the same asset the tokens themselves settle in. Every payment is a public, auditable transaction: the market's information layer becomes as transparent as its trading layer.
Next: when the delta actually pays — free tier vs real-time.
Links
- Agent guide (endpoints, limits, examples): agentbadge.xyz/bstock-guide
- Originally published on the AgentBadge blog: agentbadge.xyz/blog/bstock-arc-x402-payment
- MCP endpoint:
https://agentbadge.xyz/mcp/bstock/tools/get_delta
