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Sellers that want x402 USDC acceptance without running a relayer, funding a gas wallet, or building sanctions screening can point their HTTP API at Circle's hosted Facilitator Service.
Circle announced Facilitator Service availability around September 19, 2026 for USDC settlement on Arc, Base, and Polygon PoS via the EIP-3009 exact scheme. This guide is the seller-side verify and settle how-to for that named product, not a CDP-centric facilitator picker and not Gateway nanopayments.
Facts below come from Circle's Facilitator Service docs and the Arc testnet quickstart. No invented fees, SLA numbers, or unpublished chain IDs.
Key Takeaways
- Circle Facilitator Service is a hosted x402 facilitator that settles USDC on Arc, Base, and Polygon PoS through EIP-3009 exact transfers.
- Circle verifies buyer signatures, screens buyer and seller addresses, records payment state before broadcast, pays settlement gas, and submits the onchain transfer.
- Sellers authenticate each verify, settle, and status call with a Facilitator-Seller-Proof (EIP-712 seller proof bound to payTo).
- Production settle uses a Circle API key; Circle also documents a keyless trial on Arc testnet without a Circle account.
- Named downside: Base and Polygon PoS settlements carry reorg risk and Circle does not guarantee fund receipt there; Arc settlements are described as final.
Who this is for
Use Facilitator Service if you sell metered APIs, agent tasks, datasets, or marketplace settlement and want one Circle-hosted facilitator across Arc, Base, and Polygon PoS.
Skip this path if you only need buyer-side agent wallets (see Circle Agent Wallet) or Gateway batched nanopayments (see Circle agent nanopayments). For facilitator shopping across vendors, start with how to choose an x402 facilitator.
What Circle Facilitator Service is
Per Circle docs, Facilitator Service is Circle's hosted x402 facilitator for sellers. Point your HTTP API at it and accept x402 payments in USDC without operating a relayer, funding a gas wallet, or building your own sanctions screening.
Circle verifies each buyer-signed EIP-3009 authorization and submits the USDC transfer onchain. Circle broadcasts every transfer, pays settlement gas, and screens both parties before any money state is created.
Disclaimer from Circle: Facilitator Service is offered by Circle Technology Services, LLC as a software provider. It verifies buyer-signed EIP-3009 USDC authorizations under x402 only. It does not hold, control, or transmit user funds, verify transaction purpose, or confirm agent authority scope.
How the money path works
x402 remains HTTP-native: the seller returns 402 with payment requirements; the buyer (wallet or agent) signs and retries with a payment payload.
On Facilitator Service, /settle is the authoritative money path. It validates the authorization, screens buyer and seller, records durable payment state, submits the USDC transfer, and returns terminal evidence or a pending response.
Buyers authorize with EIP-3009 TransferWithAuthorization fields: from, to, value, validAfter, validBefore, and nonce. USDC uses 6 decimals (1 USDC = 1000000 base units in Circle's examples).
| Surface | What operators get from Circle docs |
|---|---|
| Networks | Arc, Base, and Polygon PoS (one seller integration) |
| Scheme | EIP-3009 exact USDC transfers |
| Gas | Circle pays settlement gas and broadcasts the transfer |
| Screening | Buyer and seller addresses screened before money state |
| Idempotency | payment-identifier extension (16–128 chars [A-Za-z0-9_-]) or exact same signed auth on retry |
| Auth | Facilitator-Seller-Proof header; production settle needs Circle API key; keyless trial on Arc testnet |
| Endpoints | api.circle.com/v1/facilitator/x402/settle and /status/{paymentId} |
Step 1. Confirm Facilitator Service is the right product
Read Circle's Facilitator Service overview and confirm you need seller-side verify/settle, not Gateway nanopayment batching and not Agent Wallet issuance.
Stablecoin Insider's take: if the job is "accept x402 USDC and let Circle run the relayer," Facilitator Service is the named object. If the job is sub-cent gas-free batching into a Gateway balance, stay on the nanopayments docs instead.
Step 2. Stand up a seller payTo wallet
Create an EVM wallet that will receive USDC. That address is payTo in payment requirements and in every seller proof.
You need the private key (or signing path) that controls payTo, because Facilitator Service requires an EIP-712 seller proof proving control of that address for verify, settle, and status.
Step 3. Start on Arc testnet with the keyless trial
Circle's quickstart accepts a signed x402 authorization on Arc testnet through Facilitator Service without a Circle account or API key (keyless trial).
Documented prerequisites: Node.js v22.6+, viem, a payTo wallet plus its private key, and a buyer wallet funded with Arc testnet USDC from the Circle Faucet.
Quickstart examples sign against Arc testnet chainId 5042002 and USDC verifyingContract 0x3600000000000000000000000000000000000000 with domain name USDC / version 2.
Step 4. Capture the buyer EIP-3009 authorization
In production, the buyer's wallet or agent signs TransferWithAuthorization and sends it in the x402 retry. Keep signature plus authorization fields (from, to, value, validAfter, validBefore, nonce) for /settle.
Match to to your payTo, and set value in USDC base units. Circle's sample uses 1000000 for 1 USDC.
Step 5. Build Facilitator-Seller-Proof for each call
The seller proof is a base64url-encoded envelope with an EIP-712 signature. Domain name in Circle's sample: Circle Facilitator Seller Request version 1.
Sign with purpose matching the route (verify, settle, or status), plus method, bodyHash, network (for example eip155:5042002 on Arc testnet), payTo, nonce, issuedAt, and expiresAt (sample uses a 5-minute window).
Pass the proof in the Facilitator-Seller-Proof HTTP header on every Facilitator Service call.
Step 6. Call /settle (and reconcile pending)
POST to https://api.circle.com/v1/facilitator/x402/settle with the x402 payment payload and payment requirements. Include a payment-identifier extension when you can: Circle requires id length 16 to 128 from [A-Za-z0-9_-].
Circle documents that /settle always answers HTTP 200. Terminal success returns success: true with payer, transaction hash, network, and amount. Pending returns success: false with errorReason: settlement_pending and a paymentId for /status.
Do not fulfill the paid resource on pending. A timeout is not evidence of failure. To retry, reuse the same payment-identifier, or the exact same signed buyer authorization if you omitted one. Never re-sign a fresh authorization for the same charge.
Step 7. Confirm with /status before fulfillment
Sign a fresh seller proof with purpose status, then GET https://api.circle.com/v1/facilitator/x402/status/{paymentId} until status is completed or failed.
Only after completed should your API return the paid resource. That is the same fulfill-on-settlement discipline Stablecoin Insider uses in accepting x402 USDC from AI agents.
Step 8. Move to production settle with a Circle API key
Circle states Facilitator Service requires a Circle API key to settle in production, while the keyless trial lets teams start on Arc testnet without an account.
Point the same seller integration at Arc, Base, and Polygon PoS once production credentials and network parameters are confirmed from Circle's supported-networks reference.
How this differs from nearby Circle and x402 posts
| Guide | Job to be done |
|---|---|
| This post (Facilitator Service) | Seller verify/settle via Circle-hosted x402 facilitator |
| How to choose an x402 facilitator | Compare facilitator options (often CDP-centric) |
| Circle Agent Wallet | Issue/control agent spend wallets |
| Circle agent nanopayment | Gateway batched gas-free nanopayments |
| Accept x402 from AI agents | Generic seller HTTP 402 pattern |
| Fireblocks Agentic Payments Gateway | PSP hosted facilitator into Fireblocks Vaults |
For protocol basics, see x402 protocol explained. For another managed facilitator stack, see Fireblocks Agentic Payments Gateway.
Stablecoin Insider's take
Stablecoin Insider's take: Circle is productizing the boring half of x402, verification, screening, gas, and broadcast, so sellers can stay focused on 402 surfaces and fulfillment.
Treat Arc as the finality-friendly path Circle documents most clearly in the quickstart, and treat Base/Polygon PoS reorg language as a hard product constraint in risk reviews.
Comparing facilitators before wiring Circle?
FAQ
What is Circle Facilitator Service?
It is Circle's hosted x402 facilitator for sellers. It verifies buyer-signed EIP-3009 USDC authorizations, screens addresses, records payment state, pays settlement gas, and submits the onchain transfer on Arc, Base, and Polygon PoS.
Which networks does Facilitator Service support?
Circle documents USDC settlement on Arc, Base, and Polygon PoS through the EIP-3009 exact scheme from one seller integration.
Do sellers need a gas wallet?
No for settlement gas on Facilitator Service. Circle broadcasts each transfer and pays settlement gas. Sellers still need a payTo address that can receive USDC and a signing path for Facilitator-Seller-Proof.
What is Facilitator-Seller-Proof?
A base64url envelope carrying an EIP-712 signature that proves control of payTo and binds purpose (verify, settle, or status), method, body hash, network, and time window. Pass it in the Facilitator-Seller-Proof header.
How should sellers handle settlement_pending?
Do not fulfill. Poll /status with the paymentId until completed or failed. Retry with the same payment-identifier or the exact same signed buyer authorization. Never re-sign a new authorization for the same charge.
Is the keyless trial the same as production?
No. Circle documents a keyless trial on Arc testnet without a Circle account. Production settle requires a Circle API key.
How is this different from Circle Gateway nanopayments?
Facilitator Service settles individual EIP-3009 exact transfers with Circle as the hosted facilitator. Gateway nanopayments batch authorizations into gas-free Gateway balances. Use the product that matches your settlement model.
What risks does Circle call out on Base and Polygon PoS?
Circle states settlements on Base and Polygon PoS are subject to blockchain reorganization risk and that Circle does not guarantee fund receipt on those networks. Arc settlements are described as final.
This content is provided for informational and educational purposes only and does not constitute financial, investment, legal, or tax advice; no material herein should be interpreted as a recommendation, endorsement, or solicitation to buy or sell any financial instrument, and readers should conduct their own independent research or consult a qualified professional.
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