FLUX 3 Image Klein API documentation

Name: FLUX 3 Image Klein API
Brand: Black Forest Labs
SKU: bfl/flux-3-image-klein
Availability: InStock

Everything you need to call FLUX 3 Image Klein from your code. Base URL https://cheapergen.com/api/v1. Try it first in the playground.

Using a coding agent?

Paste this into Claude Code, Cursor, Codex or any coding agent. It adds the API to your project, keeps the key in CHEAPERGEN_API_KEY and tests with a free quote before anything is spent.

Add FLUX 3 Image Klein (CheaperGen endpoint bfl/flux-3-image-klein/text-to-image) to this project by following https://cheapergen.com/agents/integrate.md

What your agent reads

Authentication

Create a key in Dashboard → API keys and send it as a bearer token. Keep keys server-side.

export CHEAPERGEN_API_KEY="cg_live_…"

# every request
Authorization: Bearer $CHEAPERGEN_API_KEY

FLUX 3 Image Klein Text to Image API

POST/api/v1/run/bfl/flux-3-image-klein/text-to-image

Submits an asynchronous job and returns 202 with a generation id. Poll GET /api/v1/generations/{id} or pass webhook_url. See job lifecycle.

Input parameters

Name	Type	Description	Affects price
`prompt`required	string	Describe the shot: subject, action, camera movement, lighting and style.	No
`aspect_ratio`	string (enum)	Output image shape. Values: 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 Default: 1:1	Yes
`resolution`	string (enum)	Output 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. Values: 768 · 1K · 1.5K · 2K · 4K Default: 1K	Yes
`seed`	integer	Use the same seed and settings to reproduce a result. Leave empty for random.	No
`enable_safety_checker`	boolean	If set to true, the safety checker will be enabled. Content our Acceptable Use Policy prohibits stays blocked either way. Default: true	No
`webhook_url`	string (URL)	Optional. We POST the finished generation here, signed with your webhook secret. Webhooks	No

Request

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);

import os, time, requests

API = "https://cheapergen.com/api/v1"
headers = {"Authorization": f"Bearer {os.environ['CHEAPERGEN_API_KEY']}"}

# 1. Submit the job
job = requests.post(f"{API}/run/bfl/flux-3-image-klein/text-to-image", headers=headers, json={
    "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"
}).json()

# 2. Poll until it finishes (or pass "webhook_url" and skip polling)
while job["status"] in ("queued", "running"):
    time.sleep(3)
    job = requests.get(f"{API}/generations/{job['id']}", headers=headers).json()

print(job["status"], job["output"]["images"][0]["url"] if job["status"] == "succeeded" else job["error"])

curl -X POST https://cheapergen.com/api/v1/run/bfl/flux-3-image-klein/text-to-image \
  -H "Authorization: Bearer $CHEAPERGEN_API_KEY" \
  -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"
}'

Response

{
  "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": "queued",
  "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": null,
  "error": null,
  "cost": {
    "amount_usd": 0.2255,
    "currency": "usd",
    "estimated": true,
    "official_usd": null,
    "list_price_source": "official",
    "list_price_label": "Official",
    "saved_usd": null
  },
  "source": "api",
  "started_at": null,
  "completed_at": null,
  "urls": {
    "get": "https://cheapergen.com/api/v1/generations/gen_8c2QmX1nq0k4",
    "cancel": "https://cheapergen.com/api/v1/generations/gen_8c2QmX1nq0k4/cancel"
  },
  "created_at": "2026-10-15T09:21:04Z"
}

{
  "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"
}

FLUX 3 Image Klein Image Edit API

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

Submits an asynchronous job and returns 202 with a generation id. Poll GET /api/v1/generations/{id} or pass webhook_url. See job lifecycle.

Input parameters

Name	Type	Description	Affects price
`prompt`required	string	Describe the shot: subject, action, camera movement, lighting and style.	No
`image_urls`required	string[] (URLs)	Up to 10 reference images to edit or combine. Refer to them as "image 1", "image 2"… in the prompt. Max items: 10	No
`aspect_ratio`	string (enum)	Output image shape. Values: auto · 1:1 · 4:3 · 3:4 · 3:2 · 2:3 · 16:9 · 9:16 · 21:9 · 9:21 Default: auto	Yes
`resolution`	string (enum)	Output size tier: 1K ≈ 1 MP, 2K ≈ 4 MP, 4K ≈ 16 MP. Values: 1K · 2K · 4K Default: 1K	Yes
`seed`	integer	Use the same seed and settings to reproduce a result. Leave empty for random.	No
`enable_safety_checker`	boolean	If set to true, the safety checker will be enabled. Content our Acceptable Use Policy prohibits stays blocked either way. Default: true	No
`webhook_url`	string (URL)	Optional. We POST the finished generation here, signed with your webhook secret. Webhooks	No

Request

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/edit`, {
  method: "POST",
  headers,
  body: JSON.stringify({
    "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"
  }),
}).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);

import os, time, requests

API = "https://cheapergen.com/api/v1"
headers = {"Authorization": f"Bearer {os.environ['CHEAPERGEN_API_KEY']}"}

# 1. Submit the job
job = requests.post(f"{API}/run/bfl/flux-3-image-klein/edit", headers=headers, json={
    "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"
}).json()

# 2. Poll until it finishes (or pass "webhook_url" and skip polling)
while job["status"] in ("queued", "running"):
    time.sleep(3)
    job = requests.get(f"{API}/generations/{job['id']}", headers=headers).json()

print(job["status"], job["output"]["images"][0]["url"] if job["status"] == "succeeded" else job["error"])

curl -X POST https://cheapergen.com/api/v1/run/bfl/flux-3-image-klein/edit \
  -H "Authorization: Bearer $CHEAPERGEN_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "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"
}'

Response

{
  "id": "gen_8c2QmX1nq0k4",
  "object": "generation",
  "model": "bfl/flux-3-image-klein",
  "endpoint": "bfl/flux-3-image-klein/edit",
  "mode": "edit",
  "status": "queued",
  "input": {
    "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"
  },
  "output": null,
  "error": null,
  "cost": {
    "amount_usd": 0.2255,
    "currency": "usd",
    "estimated": true,
    "official_usd": null,
    "list_price_source": "official",
    "list_price_label": "Official",
    "saved_usd": null
  },
  "source": "api",
  "started_at": null,
  "completed_at": null,
  "urls": {
    "get": "https://cheapergen.com/api/v1/generations/gen_8c2QmX1nq0k4",
    "cancel": "https://cheapergen.com/api/v1/generations/gen_8c2QmX1nq0k4/cancel"
  },
  "created_at": "2026-10-15T09:21:04Z"
}

{
  "id": "gen_8c2QmX1nq0k4",
  "object": "generation",
  "model": "bfl/flux-3-image-klein",
  "endpoint": "bfl/flux-3-image-klein/edit",
  "mode": "edit",
  "status": "succeeded",
  "input": {
    "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"
  },
  "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"
}

Get the result

Generations are asynchronous. Poll until status is succeeded, failed or canceled — or pass webhook_url when you submit. Failed generations are refunded automatically.

curl https://cheapergen.com/api/v1/generations/gen_8c2QmX1nq0k4 \
  -H "Authorization: Bearer $CHEAPERGEN_API_KEY"

More: job lifecycle · webhooks · errors

FLUX 3 Image Klein pricing

Pay per image as you go, with no subscription required. Failed generations are refunded automatically.

Tier	Official price	CheaperGen	You save
768 768×768	~~$0.008~~/img	$0.0011/img With a monthly plan: Max $0.001	−87%
1K 1024×1024	~~$0.009~~/img	$0.0019/img With a monthly plan: Pro $0.0018Max $0.0017	−79%
1.5K 1536×1536	~~$0.011~~/img	$0.0043/img With a monthly plan: Pro $0.004Max $0.0038	−61%
2K 2048×2048	~~$0.014~~/img	$0.0074/img With a monthly plan: Pro $0.0069Max $0.0065	−48%
4K ≈16 MP	~~$0.036~~/img	$0.0342/img	−5%
Edit 1K 1–10 reference images	~~$0.009~~/img	$0.0085/img	−6%
Edit 2K 1–10 reference images	~~$0.014~~/img	$0.0133/img	−5%
Edit 4K 1–10 reference images	~~$0.036~~/img	$0.0342/img	−5%

Monthly plans lower prices on most models (shown under each price); you can still pay as you go. Pro $499/month · Max $4,999/month.

Official price: BFL API list price for FLUX 3 Image Klein ($0.008 at 768², $0.009 at 1K, $0.011 at 1.5K, $0.014 at 2K, $0.036 at 4K; BFL charges the same for an edit) — https://docs.bfl.ai/quick_start/pricing#flux-3-image-klein. Prices verified October 18, 2026.
Editing has its own price per output size (the Edit rows: 1K, 2K or 4K), the same however many reference images (up to 10).
Served without BFL's prompt upsampler: your prompt reaches the model as written.