Fast image generation (OpenAI-compatible, budget)

Budget text-to-image over x402 - OpenAI images wire (prompt in, inline base64 out) at $0.02 per picture, a quarter of the flagship /v1/images/generations price. Send POST /v1/images/fast with the required field prompt and pay $0.020 per call over x402 with USDC on an EVM chain. It returns a JSON object with created, model, data and usage.

Served by FLUX.2 Klein 4B (about 2 seconds per image, 1024x1024 JPEG) with GPT-5 Image Mini as the failover. n locked to 1, text-to-image only, size and quality fixed. Point any OpenAI SDK's images.generate() at base_url https://agent402.tools/v1 and call /images/fast.

Category: LLM gateway · Tags: image-generation images text-to-image generate generate-image create-image picture cheap · Also found as: fast-image-generation budget-image-generation

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Parameters

Example request

curl -i -X POST https://agent402.tools/v1/images/fast \
  -H "Content-Type: application/json" \
  -d '{"prompt":"A minimalist line drawing of a lighthouse at dawn"}'

Without payment this returns HTTP 402 Payment Required with the exact price for v1-images-fast; any x402 v2 or MPP client pays it and retries.

Example response

{
  "created": 1750000000,
  "model": "black-forest-labs/flux.2-klein-4b",
  "data": [
    {
      "b64_json": "/9j/4AAQSkZJRgABAQAAAQABAAD…",
      "media_type": "image/jpeg"
    }
  ],
  "usage": {
    "prompt_tokens": 11,
    "completion_tokens": 4096,
    "total_tokens": 4107
  }
}

From an MCP client

catalog.call {
  "slug": "v1-images-fast",
  "params": {
    "prompt": "A minimalist line drawing of a lighthouse at dawn"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for v1-images-fast; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• prompt is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails.
• Wallet-only: this tool runs a model, so it has no proof-of-work tier. A prepaid card-credits key (Authorization: Bearer a402_...) also pays it.
• Model-backed: the answer is generated by a model, so the same input can produce different wording.
• Long-running: payment settles after the work finishes, so only EVM exact payments are offered.
• A GET or HEAD to /v1/images/fast returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB and a streamed response are not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/v1/images/fast", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "prompt": "A minimalist line drawing of a lighthouse at dawn"
  }),
});

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