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How to Use FLUX 3 Image Klein API

A step-by-step FLUX 3 Image Klein API tutorial with Node.js, Python and cURL: submit a text to image job, poll it or receive a webhook, and download the image. The example below costs $0.002.

Endpoints
2
Text to Image · Image Edit
Example request
$0.002
Text to Image
Languages
3
Node.js · Python · cURL
Failed runs
$0
refunded automatically
Get API keyCreate with FLUX 3 Image KleinAPI docs
1

Get an API key

Create an account, add credits and create a key in Dashboard → API keys. Store it as CHEAPERGEN_API_KEY on your server. Every request sends it as a bearer token.

How to get a FLUX 3 Image Klein API key
2

Choose a FLUX 3 Image Klein endpoint

Each task has its own endpoint. All of them take a JSON body and return a generation you can poll.

FLUX 3 Image Klein API endpoints, required inputs and prices
TaskEndpointRequiredFrom
Text to Imagebfl/flux-3-image-klein/text-to-imageprompt$0.0011/image
Image Editbfl/flux-3-image-klein/editprompt, image_urls$0.0011/image
3

Submit a text to image job

This program submits the job, polls every 3 seconds until it finishes and prints the image URL. Swap the prompt and settings for your own.

const API = "https://cheapergen.com/api/v1";
const headers = {
  Authorization: `Bearer ${process.env.CHEAPERGEN_API_KEY}`,
  "Content-Type": "application/json",
};

// 1. Submit the job
let job = await fetch(`${API}/run/bfl/flux-3-image-klein/text-to-image`, {
  method: "POST",
  headers,
  body: JSON.stringify({
    "prompt": "Editorial still life of a hand-thrown terracotta vase with dried orange ranunculus on a travertine plinth, low golden-hour sun from the left, long soft shadows on a warm plaster wall, medium-format film photograph",
    "aspect_ratio": "1:1",
    "resolution": "1K"
  }),
}).then((r) => r.json());

// 2. Poll until it finishes (or pass webhook_url and skip polling)
while (job.status === "queued" || job.status === "running") {
  await new Promise((r) => setTimeout(r, 3000));
  job = await fetch(`${API}/generations/${job.id}`, { headers }).then((r) => r.json());
}

console.log(job.status === "succeeded" ? job.output.images[0].url : job.error);
4

Set the parameters that matter

The settings for bfl/flux-3-image-klein/text-to-image, with what each one does to the price.

FLUX 3 Image Klein Text to Image parameters and their effect on price
ParameterType · defaultWhat it doesPrice effect
aspect_ratiostring (enum) · 1:1Output image shape.
1:1 · 4:5 · 3:4 · 2:3 · 9:16 · 1:2 · 9:21 · 5:4 · 4:3 · 3:2 · 16:9 · 2:1 · 21:9 · 7:5 · 5:7
1:1: $0.0011/image
resolutionstring (enum) · 1KOutput size tier: 768 ≈ 0.6 MP, 1K ≈ 1 MP, 1.5K ≈ 2.4 MP, 2K ≈ 4 MP, 4K ≈ 16 MP. Up to 2K, wide and tall ratios keep the long side at 2048 px or less; 4K takes 1:1, 4:3, 3:4, 3:2, 2:3, 16:9, 9:16, 21:9, 9:21.
768 · 1K · 1.5K · 2K · 4K
768: $0.0011/image
1K: $0.0019/image
1.5K: $0.0043/image
2K: $0.0074/image
4K: $0.0342/image
seedintegerUse the same seed and settings to reproduce a result. Leave empty for random.None
enable_safety_checkerboolean · trueIf set to true, the safety checker will be enabled. Content our Acceptable Use Policy prohibits stays blocked either way.None

Other FLUX 3 Image Klein endpoints take the same shape with their own inputs:

POST /api/v1/run/bfl/flux-3-image-klein/edit

{
  "prompt": "Put the lamp from image 2 on the desk in image 1; keep the room, the light and the camera angle",
  "image_urls": [
    "https://cdn.cheapergen.com/samples/portrait.jpg"
  ],
  "aspect_ratio": "auto",
  "resolution": "1K"
}
5

Get the result

A job moves from queued to running to succeeded, failed or canceled. Poll GET /api/v1/generations/{id}, or pass webhook_url and we POST the result to you. Download the output and store it yourself.

200 — succeeded
{
  "id": "gen_8c2QmX1nq0k4",
  "object": "generation",
  "model": "bfl/flux-3-image-klein",
  "endpoint": "bfl/flux-3-image-klein/text-to-image",
  "mode": "text-to-image",
  "status": "succeeded",
  "input": {
    "prompt": "Editorial still life of a hand-thrown terracotta vase with dried orange ranunculus on a travertine plinth, low golden-hour sun from the left, long soft shadows on a warm plaster wall, medium-format film photograph",
    "aspect_ratio": "1:1",
    "resolution": "1K"
  },
  "output": {
    "images": [
      {
        "url": "https://cdn.cheapergen.com/outputs/gen_8c2Q-0.png",
        "content_type": "image/png",
        "width": 2048,
        "height": 2048
      }
    ]
  },
  "error": null,
  "cost": {
    "amount_usd": 0.2255,
    "currency": "usd",
    "estimated": false,
    "official_usd": 0.264,
    "list_price_source": "official",
    "list_price_label": "Official",
    "saved_usd": 0.0385
  },
  "source": "api",
  "created_at": "2026-10-15T09:21:04Z",
  "started_at": "2026-10-15T09:21:06Z",
  "completed_at": "2026-10-15T09:22:31Z"
}
Verify webhook signatures
6

Price a request before you run it

The quote endpoint is free and needs no key. It returns the price, the official price and your discount for exactly the input you send.

curl -X POST https://cheapergen.com/api/v1/quote/bfl/flux-3-image-klein/text-to-image \
  -H "Content-Type: application/json" \
  -d '{"prompt":"Editorial still life of a hand-thrown terracotta vase with dried orange ranunculus on a travertine plinth, low golden-hour sun from the left, long soft shadows on a warm plaster wall, medium-format film photograph","aspect_ratio":"1:1","resolution":"1K"}'
API errors and what to do
StatusCodeMeaning
400invalid_requestA parameter is missing or out of range — the message names it.
401unauthorizedMissing, malformed or revoked API key.
402insufficient_balanceNot enough credits for the quoted price; top up or enable auto top-up.
429rate_limitedToo many requests or generations in progress; back off and retry.
502upstream_errorThe model provider failed; the hold is refunded and you can retry.
503model_unavailableNo healthy route right now; retry later or pick another model.
Full FLUX 3 Image Klein API documentation

FAQ

FLUX 3 Image Klein API questions

No. The API is plain HTTPS with JSON, so the Node.js (fetch) and Python (requests) examples on this page are complete programs. Any language that can send an HTTP request works.

Yes. Add "webhook_url" to the request body and we POST the finished generation to it, signed with a CheaperGen-Signature header (HMAC-SHA256 of the timestamp and raw body). Polling GET /api/v1/generations/{id} works too.

Pass public URLs in "image_urls". Files without a public URL can be uploaded first with POST /api/v1/uploads, which returns a URL to use in the request.

Text to Image starts at $0.0011/image; the example request on this page costs $0.002, 79% below the official price. Failed generations are refunded automatically.