Paying for the REST gauntlet (x402)

AlphaAssay's x402 surface is exactly POST /x402/v1/gauntlet — a REST payment path, not a wrapper around every MCP tool. It needs no account or API key. x402 revives the HTTP status code 402 Payment Required as a machine-to-machine payment handshake.

How does the x402 payment handshake work?

Your agent calls that gauntlet route like any HTTP API; the first response is 402 Payment Required carrying a machine-readable price quote; the agent attaches a USDC payment authorization and retries; the completed gauntlet result comes back with a named x402_receipt. No account, no API key, no card form — four steps, settled on-chain.

step	what happens
1 · request	your agent calls `POST /x402/v1/gauntlet`
2 · quote	the response is `402` with a machine-readable price quote — the exact amount, before anything is charged
3 · pay & retry	the agent attaches the payment authorization and retries; settlement is on-chain (USDC), typically cents
4 · result	the gauntlet result plus its named payment receipt — you paid for a completed trial, not for access

What if the response gets lost — do I pay twice?

No. Every x402 payment nonce is idempotent: the same nonce with the same input re-delivers the cached response without a second settlement — one payment buys one result — and the same nonce with a different input is refused. The x402_receipt binds payment id, input digest and verdict digest. Its own signed field is authoritative: it carries Ed25519 signature fields when the deployment signing key is configured and reports signed:false otherwise. Fresh throwaway wallets inherit a conservative prior until they have settlement history — a new wallet cannot reset a family's trial budget.

What does it cost?

The exact current quote comes from https://api.alphaassay.com/v1/meta/pricing and the route's 402 response. The human-readable table is on pricing. The free tier (specimens, calibration record, certificate checks) never requires payment.

What does a paid call look like in code?

python · any x402-capable client

# the x402 client reads the gauntlet route's 402 quote, pays and retries:
# the client reads the 402 quote, pays (USDC), retries. You see the verdict.
r = x402_session.post("https://api.alphaassay.com/x402/v1/gauntlet",
                      json=my_signal)
verdict = r.json()

# the quote is visible before paying, if you want to gate on price:
q = requests.post(url, json=my_signal)      # → 402 + machine-readable quote
if quote_amount(q) <= my_budget:
    r = pay_and_retry(q)

What if I want an API key instead of x402?

The hosted public MCP server uses an api_key tool argument; bearer-authenticated REST uses its own routes and headers. Those transports share application operations where documented, but their request shapes and limits are not universally identical. Start here for an account, and check the live pricing endpoint before calling.