Build with USDF.

USDF is the dollar of the machine economy: the dollar agents pay with, and the dollar compute is priced in.

Every other way to buy compute turns money into credits: a fee to get in, locked to one platform, no way back out, earning nothing. USDF stays money. Every USDF is backed 1:1 by USDG in a stock contract with no admin keys, redeemable at any time, with no fee in and no fee out. Spend it on 100+ models, send it, borrow against it, or stake it as sUSDF and earn from the whole network.

Foundry issues USDF, the dollar of the machine economy: backed 1:1 by Paxos USDG in a stock contract, zero fees, redeemable any time, spent per request on 100+ models by people, apps and agents, and staked as sUSDF to earn from the whole network. No owner, no admin keys, and the reserve is public.

USDF is a dollar for compute on Robinhood Chain. 1 USDF = $1 of compute, redeemable 1:1 for USDG at any time.

The gateway at https://api.usdf.fi serves chat, embeddings, images, speech, transcription, rerank and video through one OpenAI-compatible API. Every request is metered in USDF and returns a receipt.

200+ agents run on USDF. They pay for their own compute per request, from a wallet or from a balance with spend limits.

There are two ways to pay. Pay per request needs no account and no key: ask for a quote, sign one payment, send the request again. A prepaid balance with API keys suits sustained volume.

Every surface, its address and what it takes:

The chain and the token, read live from the gateway:

Samples use <model>, the first available chat model.

You need a wallet on Robinhood Chain that holds USDF or USDG. No USDF yet? Buy it on the Buy page, or swap any token for it. Payments cost no gas: the gateway submits every transfer.

Paying in USDF needs a one-time approval to Permit2. That approval is the only transaction you send, and it needs a little ETH on Robinhood Chain for gas. Paying in USDG needs no approval and no gas.

1. Ask for a quote

Send the request with no credentials. The gateway answers 402 with the exact amount and the two payments it accepts. An unpaid quote costs nothing.

curl -i https://api.usdf.fi/x402/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "<model>",
    "messages": [{"role": "user", "content": "Hello"}],
    "max_tokens": 64
  }'

402 Payment Required
payment-required: <base64 JSON: x402Version, resource, accepts>
www-authenticate: Payment id="…", method="evm", intent="charge", …

{
  "error": { "message": "payment required", "type": "payment_required", "code": "x402" },
  "quote": {
    "model": "<model>",
    "max_tokens": 64,
    "price_version": "<price sheet>",
    "amount": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
    "accepted": [
      { "symbol": "USDF", "method": "permit2" },
      { "symbol": "USDG", "method": "eip3009" }
    ]
  },
  "x402": { "x402Version": 2, "accepts": [ … ] }
}

2. Pay and send

Sign one of the accepted payments and send the identical request with it. The TypeScript SDK does both steps for you, and pays in USDF when the wallet has approved Permit2, otherwise in USDG.

curl https://api.usdf.fi/x402/v1/chat/completions \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <encoded payment>" \
  -d '{
    "model": "<model>",
    "messages": [{"role": "user", "content": "Hello"}],
    "max_tokens": 64
  }'

<encoded payment> is the signed payment, base64-encoded JSON. How to sign it.

3. Read the answer and its receipt

The answer is a normal chat completion with a receipt. The quote is what you pay. The metered cost is reported beside it.

{
  "id": "<request_id>",
  "choices": [ … ],
  "receipt": {
    "request_id": "<request_id>",
    "paid": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
    "usage_cost": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
    "payment": { "tx": "<transaction hash>", "asset": "USDF", "method": "permit2" },
    "settlement": { "scheme": "x402 exact", "network": "eip155:<chain-id>" }
  }
}

Next: every payment detail and every paid endpoint

Use a prepaid balance and API keys for sustained volume. Requests are held, charged and receipted against the balance.

1. Sign in and create a key

Sign in, then create a key on the dashboard. A key starts with sk_ and is shown once. Store it as USDF_API_KEY.

2. Fund the balance

Send USDF from your linked wallet, add USDG without gas, or buy on the Buy page. Every way is in Fund the balance.

3. Set the base URL

Point any OpenAI-compatible client at:

https://api.usdf.fi/v1

4. Send a request

curl https://api.usdf.fi/v1/chat/completions \
  -H "Authorization: Bearer $USDF_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "<model>",
    "messages": [{"role": "user", "content": "Hello"}],
    "max_tokens": 256
  }'

{
  "id": "<request_id>",
  "object": "chat.completion",
  "model": "<model>",
  "choices": [ … ],
  "usage": { "prompt_tokens": …, "completion_tokens": … },
  "receipt": {
    "request_id": "<request_id>",
    "status": "ok",
    "cost": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
    "balance": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
    "settlement": {
      "status": "unsettled",
      "lookup": "https://api.usdf.fi/v1/receipts/<request_id>"
    }
  }
}

Next: keys, caps and balances

Next: the full API reference

Authentication

Each credential goes in one header. Keys are stored only as a hash.

Holds and charges

The ledger is the gateway's record of every balance, hold and charge. Spend in it settles onchain in batches; see Settlement.

• Before a request runs, a hold for its worst case is taken: the prompt plus max_tokens.
• The charge is the provider's reported usage at the sheet price, rounded up to the unit. The rest of the hold is released.
• A request that fails after its hold is marked failed_refunded, with cost zero.

Paid per request, the quote is the charge. Each price sheet promises its rates for 30 days.

Receipts

Every response carries a receipt:

• Its id is the x-request-id header. On a chat or text completion it is also the response's id.
• A response that is not streamed also sends the cost in x-cost-units. A chat or text completion paid per request does not: read receipt.paid.
• A stream sends the receipt as its last comment line, before [DONE].

"receipt": {
  "request_id": "<request_id>",
  "model": "<model>",
  "status": "ok",
  "usage": { "prompt_tokens": …, "completion_tokens": … },
  "price": { "version": "<price sheet>", "input": …, "output": … },
  "cost": { "units": "<units>", "usd": "<usd>", "usdf": "<usdf>" },
  "settlement": { "status": "unsettled", "next_batch_after": "<time>" }
}

Look one up with GET /v1/receipts/{id} and the key that made it, or with GET /x402/v1/receipts/{id} and no key at all.

Next: receipts, settlement and the public log

Units

Every amount is an integer number of units. USDF and USDG both have 6 decimals.

Amounts come back as { "units", "usd", "usdf" } strings, so no precision is lost. Prices are per 1M tokens for text, embeddings and rerank, per million characters for speech, per minute for transcription, per image unit for images and per second for video. Each model's unit is in GET /v1/pricing.

Every figure below is read live from GET /v1/limits. A request over its limit gets 429, the error code shown, and Retry-After in seconds.

Other public reads and jobs carry their own limits:

Session and dashboard calls have per-account limits too. They are listed in Account limits.

A refused request has this shape, on every endpoint:

{ "error": { "message": "…", "type": "…", "code": "…" } }

type is the class of error and code the exact reason. The common ones:

Next: status codes and error codes by area

Every docs page, by what you are doing:

Does USDF change in price?

1 USDF = $1 of compute, redeemable 1:1 for USDG at any time. At the token contract the rate never moves: anyone can wrap USDG into USDF and redeem USDF for USDG 1:1, with no fee. USDF also trades in the USDF/USDG pool on Uniswap, where the market sets the price and it can differ from 1:1; the contract's 1:1 is there beside it at any time. Redemption depends on USDG transfers succeeding: USDG is issued by a regulated issuer that retains pause and freeze powers over its own token.

Does USDF expire?

No.

Do I need an account?

No. Pay per request with a wallet and nothing else.

Which clients work?

Any OpenAI chat completions client, the AI SDK, LangChain, and any MCP client. See SDKs and MCP.

Is the Responses API served?

No. Use chat completions. Where a library offers both, pick the chat completions path.

How is the reserve verified?

Read it live on Transparency, or run every check in your browser on Verify.