USDG on Robinhood Chain / x402

APIs your agent can pay for.

Farebox is a pay-per-request API on Robinhood Chain. Your agent asks, Farebox answers 402 with a price, the agent signs once, and Farebox settles the USDG on-chain and pays the gas. No keys, no accounts, nothing held in custody.

Building an agentPay per request from code, no API key. Just trying it5 free requests a day, no wallet.
FAREBOXx402 v2 · Robinhood Chain

Sample exchange

Settled

Keep this receipt. It lives on-chain anyway.

— requests served through the router (— in the last 24 h), last one —. On-chain: — settlements, — USDG moved on Robinhood Chain.

Refreshes every 15 s · median latency — · full log on the status page.

POST /api/v1/chatThe agent asks like any HTTP client would.
402 Payment RequiredFarebox names the price. Nothing has moved yet.
HTTP/1.1 402 Payment Required
PAYMENT-REQUIRED: base64 of ↓

{
  "x402Version": 2,
  "accepts": [{
    "scheme":  "exact",
    "network": "eip155:4663",
    "amount":  "1000",          // 0.001 USDG
    "asset":   "0x5fc5…d168",      // USDG on Robinhood Chain
    "payTo":   "0xYourMerchantAddress",
    "maxTimeoutSeconds": 120,
    "extra":   { "assetTransferMethod": "permit2" }
  }]
}

The 402 is the invoice. It names the exact amount, asset, recipient and how long the offer stands. Any x402 client reads it and pays without a human.

POST /api/v1/chat PAYMENT-SIGNATURE: …The agent retries with a signed authorization attached.
PAYMENT-SIGNATURE: base64 of ↓

{
  "permit2Authorization": {
    "from":      "0xAgent",
    "permitted": { "token": "0x5fc5…d168", "amount": "1000" },
    "spender":   "0x4020…0001",   // x402 Permit2 proxy
    "nonce":     "…",
    "deadline":  "",
    "witness":   { "to": "0xYourMerchantAddress",
                   "validAfter": "0", "extra": "0x" }
  },
  "signature": "0x…"      // EIP-712, PermitWitnessTransferFrom
}

A Permit2 signature, not a transaction. It's bound to one token, one amount, one recipient and a short deadline. After a one-time approval the agent pays no gas and holds only USDG.

Farebox checks the signed payment and settles it. Two steps, then one transaction.
Signature, amount, recipient, window and balance are checked; the transfer is simulated.
POST /verify
Nothing has changed on-chain. Safe to run the request now.
{ "isValid": true, "payer": "0xAgent" }
Verified again, simulated, then the Permit2 transfer is broadcast on Robinhood Chain. The relayer pays the gas.
POST /settle
Returned once the receipt lands, usually within seconds; Farebox waits up to 60 s.
{ "success": true, "transaction": "0x…" }
0.001 USDG, agent → Farebox

One transfer, agent to Farebox. Nothing is held in escrow. A replayed signature is refused: the Permit2 nonce is spent on-chain.

200 OK PAYMENT-RESPONSE: …The response the agent asked for, with a receipt in the header.
HTTP/1.1 200 OK
PAYMENT-RESPONSE: base64 of { "success": true, "transaction": "0x…", "network": "eip155:4663" }

{
  "model": "farebox-router",
  "choices": [{ "message": { "role": "assistant", "content": "…" } }]
}

The whole exchange is two round-trips. The agent's HTTP client did it without a human, an account, or an API key.

Free to test. Paid per request.

No plans, no cards, no accounts. Each request is one small USDG payment, and every IP gets a daily allowance to try it with nothing at all.

Holders: free access · coming soon
Hold a set amount of the token and requests stop costing anything. The threshold is announced with the token; until then every request is paid or within the daily allowance.
Robinhood Chain: pay per request
0.005 USDG per completion, paid in the request itself. Farebox pays the gas.
Prepaid key: 1, 5 or 20 USDG
You fund a fbx_sk_… key once on the demo page; your agent spends it at 0.005 USDG per request with Authorization: Bearer. No wallet in the agent, top up any time.
Every IP: 5 free router requests a day
Send Farebox-Free: 1 and the router answers without an invoice until the allowance is spent.

The Farebox router

An OpenAI-compatible chat endpoint, priced per completion. Drop-in for any client that speaks x402.

endpoint
POST /api/v1/chat
price
0.005 USDG per request
free
5 per IP per day
shape
{ messages, max_tokens } → choices[0].message
Ask it somethingRouter docs

Twenty lines, and your agent pays as it goes.

Standard x402 packages. The client handles 402 → sign → retry inside fetch. USDG on Robinhood Chain isn't an SDK default yet, so the asset is spelled out; it pays through Permit2, so the wallet approves Permit2 once.

agent.ts
import { privateKeyToAccount } from 'viem/accounts';
import { x402Client, wrapFetchWithPayment }
  from '@x402/fetch';
import { ExactEvmScheme } from '@x402/evm/exact/client';

const account = privateKeyToAccount(process.env.AGENT_KEY);
const USDG = '0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168';
const NETWORK = 'eip155:4663';

const client = x402Client.fromConfig({
  schemes: [{ network: NETWORK,
              client: new ExactEvmScheme(account) }],
  spendControls: { allowedAssets: [{
    network: NETWORK, asset: USDG, maxAmountPerPayment: '100000',
  }] },
});

const pay = wrapFetchWithPayment(fetch, client);
const res = await pay('…/api/v1/chat', {
  method: 'POST',
  headers: { 'content-type': 'application/json' },
  body: JSON.stringify({ messages: [{ role: 'user', content: 'hi' }] }),
});
// 402 → sign → retry → 200, handled inside pay()
with an API key · OpenAI SDK
import OpenAI from 'openai';

const client = new OpenAI({
  baseURL: '…/api/v1',
  apiKey: 'fbx_sk_…',           // funded once on /demo
});

const r = await client.chat.completions.create({
  model: 'farebox-router',
  messages: [{ role: 'user', content: 'hi' }],
});
console.log(r.choices[0].message.content);
curl · free allowance
curl …/api/v1/chat \
  -H 'Farebox-Free: 1' \
  -H 'content-type: application/json' \
  -d '{"messages":[{"role":"user","content":"hi"}]}'

# 200 OK
# Farebox-Free-Remaining: 4
# {
#   "model": "farebox-router",
#   "choices": [{ "message": { "role": "assistant", "content": "…" } }]
# }
#
# once the allowance is spent, the same call is 402
# and any x402 client pays 0.005 USDG per request

A standard x402 facilitator does the settling.

Farebox runs its own. These four endpoints are what the payment SDKs talk to; you never call them yourself.

  • POST
    /verify

    Check a signed payment. No gas, nothing changes on-chain.

  • POST
    /settle

    Verify again, simulate, then broadcast the Permit2 transfer.

  • GET
    /supported

    Payment kinds, networks and the relayer that signs settlements.

  • GET
    /health

    RPC reachability and latest block for each Robinhood Chain network.

Networks

Farebox settles USDG, the Global Dollar, on Robinhood Chain. Gas is ETH and the relayer pays it, so a payer only holds USDG.

Non-custodial
Each payment is one on-chain transfer, agent to Farebox. Nothing sits in escrow, nothing is pre-loaded.
No API keys, no accounts
The signature is the credential. There is nothing to sign up for and nothing to leak.
Gas paid for you
Robinhood Chain prices gas in ETH. The Farebox relayer pays it on every settlement, so an agent only ever needs to hold USDG.
Simulated before it's sent
A transfer that would fail is refused at /verify. It never becomes a reverted transaction.

The token

Farebox is getting its own token on Robinhood Chain, the same network every request settles on. It is not needed to use the API today: requests are paid in USDG, and the free allowance costs nothing. First use, coming soon: hold a set amount and your requests are free. The threshold, contract address and buy link are announced here and on X first.

Until an address is shown on this page, no address claiming to be the token is ours. Treat anything else as a scam.

Buy · not live yet Follow on X
network
Robinhood Chain (eip155:4663)
needed to use Farebox
no · pay in USDG
status
not launched
use cases
free API access for holders · coming soon

Give your agent the URL.

Start with the free allowance, then pay per request or fund a key. Everything settles on Robinhood Chain.

…/api/v1/chat
Try it free Agent quickstart