Security and verification.

Every request returns a receipt: what was billed, at which price, and where it settles.

The same receipt appears in five places:

• The JSON body, as receipt.
• A stream's last comment line, : receipt {…}.
• The x-request-id header, with the cost in x-cost-units on a response that is not streamed. A chat or text completion paid per request carries receipt.paid instead.
• GET /v1/receipts/{id}, with the key that made the request.
• The MCP receipt tool.

"receipt": {
  "request_id": "<request_id>",
  "model": "<model>",
  "provider": "<provider>",
  "status": "ok",
  "usage": { "prompt_tokens": …, "completion_tokens": …, "cached_tokens": … },
  "price": { "version": "<price sheet>", "input": …, "output": … },
  "cost": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
  "balance": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
  "data_policy": { … },
  "settlement": {
    "status": "unsettled",
    "next_batch_after": "<time>",
    "lookup": "https://api.usdf.fi/v1/receipts/<request_id>"
  }
}

Looked up later, the receipt adds when it was made and its log status:

curl https://api.usdf.fi/v1/receipts/<request_id> \
  -H "Authorization: Bearer $USDF_API_KEY"

{
  "request_id": "<request_id>",
  "model": "<model>",
  "provider": "<provider>",
  "status": "ok",
  "created_at": "<time>",
  "usage": { "prompt_tokens": …, "completion_tokens": …, "cached_tokens": … },
  "price_version": "<price sheet>",
  "cost": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
  "settlement": { "status": "unsettled", "next_batch_after": "<time>" },
  "log": {
    "status": "published",
    "anchored_by": null,
    "proof": "https://api.usdf.fi/v1/log/proof/<request_id>"
  }
}

Every field:

A partial receipt was cut short and is billed for what was produced. A failed_refunded one costs zero.

Pay-per-request receipts

A request paid per request carries the payment too:

• paid: what the request was charged, what it used at the quoted price; usage_cost: the metered cost of its usage; refund: the rest of the payment, sent back in the asset paid.
• payment: tx, explorer, payer, amount (the quote, paid up front), asset and method.
• settlement.scheme: x402 exact, or mpp evm charge, with the network.
• On non-chat endpoints, modality, endpoint and billed, plus lookup.

The receipt of any request, keyed or paid per request, is public with no key. It publishes nothing the log does not.

curl https://api.usdf.fi/x402/v1/receipts/<request_id>

A USDG payment, or a refund, has settlement none: its own payment transaction is the onchain record. A USDF payment undergoes supply reduction in a later settlement batch with the rest of the spend.

Private-tier receipts

A private-tier request is tied to the provider's own signed receipt. Its data_policy.attestation starts pending, then turns verified or failed.

GET /v1/privacy/receipts/{id}, with the same key, returns the provider's archived receipt byte for byte, with its hash. See Private inference.

GET /v1/receipts lists the latest receipts, newest first, with limit, before, model and status.

A key lists its own requests. A session lists the account's. Naming another key gets 403 key_scope.

curl "https://api.usdf.fi/v1/receipts?limit=20" \
  -H "Authorization: Bearer $USDF_API_KEY"

curl https://api.usdf.fi/v1/receipts/<request_id> \
  -H "Authorization: Bearer $USDF_API_KEY"

{
  "data": [
    {
      "request_id": "<request_id>",
      "created_at": "<time>",
      "model": "<model>",
      "cost": { … },
      "status": "ok",
      "settlement": { "status": "unsettled", … },
      "receipt": "https://api.usdf.fi/v1/receipts/<request_id>"
    }
  ],
  "page": { "next_before": "<before>" }
}

Spend settles onchain in batches. A receipt's settlement.status moves through these states:

A batch runs hourly, or sooner once 50 USDF unsettled has built up. Its transaction applies supply reduction to the batch's spent USDF, releases the same USDG to the revenue wallet, and carries the batch digest and a log checkpoint in its calldata.

"settlement": {
  "batch": "<batch>",
  "status": "confirmed",
  "tx_hash": "<transaction hash>",
  "explorer": "…",
  "rows": "https://api.usdf.fi/v1/settlements/<batch>"
}

GET /v1/settlements lists batches. GET /v1/settlements/{batch} lists every row in one, with recomputed_digest and digest_matches, so anyone can check that the digest onchain commits to exactly those requests. Every settlement is on Transparency. For now both leave out each batch's amounts and rows; the transaction and the digest stay.

Every request, keyed or paid per request, is a leaf in an RFC 6962 Merkle log. Its roots are anchored onchain by the settlement transactions.

curl https://api.usdf.fi/v1/log/proof/<request_id>

The log publishes figures, never content. See Privacy and data handling.

Three more public reads let anyone check the money:

Verify runs these checks in your browser against the chain, and Transparency shows the reserve live.

• Global Dollar (USDG), issued by Paxos, retains pause and freeze powers over its own token.
• Account balances are custodial: USDF that funds an API balance is held in the gateway's wallets until it is spent or withdrawn.
• The token contract is a stock OpenZeppelin wrapper you can verify yourself. The gateway and this deployment have not had a third-party audit.
• Holder earnings depend on network revenue.