Image

FLUX 3 Image Klein API

FLUX 3 Image Klein is the 5.6B-parameter open-weights model in Black Forest Labs' FLUX 3 Image family. Call the FLUX 3 Image Klein API with model flux-3-image-klein to generate or edit one image per request from text or up to 10 references.

Open WeightsImage GenerationUp to 10 ReferencesFive Resolution Tiers

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Service Highlights

Official Discounts
Pay-as-you-go
Fast & Low Latency

Input

Model

Reference Image

Prompt

Resolution

Aspect Ratio

Sampling Steps

Output Format

Seed

Safety tolerance

Output

Image link valid for 72 hours

FLUX 3 Image Klein API Pricing

Transparent pricing with no hidden fees. Pay only for what you use.

* Actual costs are subject to final output.

FLUX 3 Image Klein API for Image Generation and Editing

The FLUX 3 Image Klein API lets you generate images from text, edit a reference or combine up to 10 images. Pick a resolution tier and aspect ratio, and control seed, steps, output format and safety tolerance.

FLUX 3 Image Klein is the smaller, faster open-weights model in the FLUX 3 Image family. Compare with FLUX 3 Image

FLUX 3 Image Klein API Capabilities

Generation, editing and output controls available in the FLUX 3 Image Klein API

Text-to-Image with FLUX 3 Image Klein

Describe the subject, composition, lighting and style to create a new image.

Editing and Multi-Reference in the FLUX 3 Image Klein API

Edit one image or combine up to 10 references; the first reference is the image being edited.

FLUX 3 Image Klein Resolution Tiers

Choose 768sq (768×768), 1k (~1 MP), 1.5k (~2 MP), 2k (~4 MP) or 4k (~16 MP).

Aspect Ratios for FLUX Klein

Choose from 15 ratios or auto. When editing, auto follows the first reference image.

Bounding-Box Layouts with FLUX 3 Klein

Place elements on a 0–1000 grid with boxes written in the prompt, and edit several regions while keeping the rest unchanged.

Seed and Steps in the FLUX 3 Image Klein API

Set a seed to reproduce results and choose 1–16 denoising steps; the default is 16.

PNG or JPEG Output from flux-3-image-klein

Return results as JPEG (default) or PNG.

Safety Tolerance for the FLUX 3 Image Klein API

Set safety_tolerance from 0 to 4, with 0 strictest and 2 by default.

FLUX 3 Image Klein API Use Cases

How creative, product and design teams use the FLUX 3 Image Klein model

Fast Concept Drafts with FLUX 3 Image Klein

Iterate on composition ideas quickly, then refine the chosen draft with more steps or a higher resolution.

Product Photo Edits with the FLUX 3 Image Klein API

Change specific elements of a product photo with bounding boxes while keeping the rest unchanged, then review details before use.

Banner and Screen Formats with FLUX Klein

Pick a wide or tall aspect ratio such as 21:9 or 9:16, then the resolution tier you need for banners, covers or app screens.

Style and Reference Mixing via the Klein API

Combine up to 10 references, for example to apply the style of one image to another.

Reproducible Variations with a Fixed Seed

Keep the seed fixed and adjust the prompt to compare controlled variations.

Typography and Design Drafts with FLUX 3 Image Klein

Explore posters and graphic layouts with text, and check final copy and brand requirements separately.

How to Get a FLUX 3 Image Klein API Key and Start Building

Three steps from sign-up to your first FLUX 3 Image Klein API request

Create an APIMart Account

→

Add Credits

Top up your balance. FLUX 3 Image Klein is billed per image by resolution tier, and the same balance works across all models.

→

Get Your API Key

Create an API key in the dashboard and send it as a Bearer token to POST /v1/images/generations with model flux-3-image-klein.

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FLUX 3 Image Klein API Example: Text to Image and Image Editing

Call flux-3-image-klein with one POST request. Generation is asynchronous: submit a task, then poll the task endpoint for the image URL.

1
Authenticate FLUX 3 Image Klein API requests
Save your APIMart key in the APIMART_API_KEY environment variable and send it as Authorization: Bearer <key> on every request.
2
Submit a FLUX 3 Image Klein task
POST /v1/images/generations with model flux-3-image-klein, your prompt, resolution and aspect_ratio. Add seed, steps or output_format if needed, and image_urls to edit. The example.com URLs are placeholders: replace them with your own publicly accessible images or Base64 data. The task ID is in data[0].task_id.
3
Get the FLUX 3 Image Klein result
Poll GET /v1/tasks/{task_id} until status is completed, then read the image URL from data.result.images[0].url[0]. APIMart keeps results for 72 hours, so download the images you want to keep.
See the FLUX 3 Image Klein API reference for every parameter, layout syntax and response field.

POST /v1/images/generations

curl -X POST https://api.apimart.ai/v1/images/generations \
  -H "Authorization: Bearer $APIMART_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "flux-3-image-klein",
    "prompt": "Flat vector poster of a mountain sunrise, bold title text SUMMIT 2026, warm orange and teal palette",
    "resolution": "1k",
    "aspect_ratio": "16:9",
    "output_format": "png"
  }'

import os
import time
import requests

API_BASE = "https://api.apimart.ai"
headers = {"Authorization": f"Bearer {os.environ['APIMART_API_KEY']}"}

# 1. Submit the generation task
payload = {
  "model": "flux-3-image-klein",
  "prompt": "Flat vector poster of a mountain sunrise, bold title text SUMMIT 2026, warm orange and teal palette",
  "resolution": "1k",
  "aspect_ratio": "16:9",
  "output_format": "png"
}
resp = requests.post(f"{API_BASE}/v1/images/generations", headers=headers, json=payload, timeout=60)
resp.raise_for_status()
task_id = resp.json()["data"][0]["task_id"]

# 2. Poll the task until it finishes
for _ in range(200):
    task_resp = requests.get(f"{API_BASE}/v1/tasks/{task_id}", headers=headers, timeout=30)
    task_resp.raise_for_status()
    task = task_resp.json()["data"]
    if task["status"] == "completed":
        print(task["result"]["images"][0]["url"][0])
        break
    if task["status"] == "failed":
        raise RuntimeError(task.get("error", {}).get("message", "generation failed"))
    time.sleep(3)
else:
    raise TimeoutError(f"task {task_id} did not finish in time; continue GET polling with this task ID")

curl -X POST https://api.apimart.ai/v1/images/generations \
  -H "Authorization: Bearer $APIMART_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "flux-3-image-klein",
    "prompt": "Turn the photo into a watercolor illustration and keep the composition and the people'\''s poses",
    "resolution": "1k",
    "aspect_ratio": "auto",
    "image_urls": [
      "https://example.com/reference.jpg"
    ]
  }'

TASK_ID="task_xxx"  # replace with the task_id returned by the POST request
curl "https://api.apimart.ai/v1/tasks/$TASK_ID" \
  -H "Authorization: Bearer $APIMART_API_KEY"

FLUX 3 Image Klein API Parameters

Parameter	Type	Required	Default	Description
`model`	string	Required	Default: flux-3-image-klein	Use flux-3-image-klein.
`prompt`	string	Required	Default: —	Scene description for text-to-image, or edit instructions. Negative prompts are not supported; describe what you want to see.
`image_urls`	string[]	Optional	Default: —	Up to 10 reference images as public HTTP(S) URLs or Base64. Omit for text-to-image; the first image is the one being edited.
`resolution`	string	Optional	Default: 1k	768sq, 1k, 1.5k, 2k or 4k (about 16 MP). Sets the price per image.
`aspect_ratio`	string	Optional	Default: auto	One of 15 ratios from 21:9 to 9:21, or auto. Pixel sizes such as 1024x1024 return HTTP 400.
`seed`	integer	Optional	Default: —	0 to 4294967295. Reuse the same seed and settings to reproduce a result; omit for a random seed.
`steps`	integer	Optional	Default: 16	1 to 16 denoising steps. Fewer steps are faster; the price does not change.
`output_format`	string	Optional	Default: jpeg	jpeg or png (jpg equals jpeg). webp returns HTTP 400.
`safety_tolerance`	integer	Optional	Default: 2	0 (strictest) to 4.

Compare FLUX API Models on APIMart

One APIMart API key calls every FLUX model below. Image models are billed per image and FLUX 3 Video per second of video.

Model	Best for	Output
FLUX 3 Image API	The FLUX 3 API for images: generation and editing with up to 10 references, search grounding and output up to 4K	768sq to 4K (about 16 MP)
FLUX 3 Image Klein APIThis page	Lower-cost FLUX 3 images with seed, 1–16 steps and PNG or JPEG output	768sq to 4K (about 16 MP)
FLUX 3 Video API	Text to video, 1–10 keyframes, video continuation and drafts, with synced audio	HD or FHD, 5–20 s
FLUX.2 API	Choosing between FLUX.2 Pro, Max and Flex on one page	1–4 MP
FLUX.2 Pro API	Balanced quality and cost for production images, up to 8 references	1–4 MP
FLUX.2 Max API	The highest-quality FLUX.2 output, up to 8 references	1–4 MP
FLUX.2 Flex API	Adjustable steps and guidance for typography and layout-heavy designs	1–4 MP
FLUX.1 Kontext API	Choosing between FLUX.1 Kontext Pro and Max on one page	About 1 MP
FLUX.1 Kontext Pro API	Context-aware edits at a fixed price per image, up to 4 references	About 1 MP
FLUX.1 Kontext Max API	Higher-quality Kontext edits with stronger prompt adherence	About 1 MP

FLUX 3 Image Klein API FAQ

Common questions about the FLUX 3 Image Klein API: model, inputs, pricing, API key and task handling

What is the FLUX 3 Image Klein API?

The FLUX 3 Image Klein API gives you access to the 5.6B-parameter open-weights model in Black Forest Labs' FLUX 3 Image family. On APIMart, use model flux-3-image-klein for text-to-image, editing or multi-reference work. Each request returns one image.

When was FLUX 3 Image Klein released?

Black Forest Labs released FLUX 3 Image Klein on October 15, 2026, as open weights and through its API, two weeks after FLUX 3 Image. On APIMart you call it with model flux-3-image-klein.

How is FLUX 3 Image Klein different from FLUX 3 Image?

Klein is the smaller, faster and lower-cost model in the family. Through the API it also accepts seed, 1–16 steps and PNG or JPEG output. It does not support the grounding search option of FLUX 3 Image, and safety_tolerance uses the same 0–4 range.

How many reference images does the FLUX 3 Image Klein API accept?

image_urls accepts up to 10 HTTP(S) URLs or base64 images. The first image is the one being edited.

Which sizes does the FLUX 3 Image Klein API support?

Choose a resolution tier — 768sq (768×768), 1k (~1 MP), 1.5k (~2 MP), 2k (~4 MP) or 4k (~16 MP) — with auto or one of 15 aspect ratios. width and height are not accepted at the moment; for a specific frame, combine aspect_ratio with resolution.

What do seed, steps and output_format do in FLUX 3 Image Klein?

seed (0 to 4294967295) makes results reproducible with the same settings; leave it empty for a random seed. steps sets 1 to 16 denoising steps (default 16); fewer steps are faster and don't change the price. output_format returns jpeg (default) or png, and jpg is treated as jpeg.

Can I use the FLUX 3 Image Klein open weights commercially?

Black Forest Labs publishes the Klein weights on Hugging Face under the license on its model card. According to Black Forest Labs, running the weights in a commercial product requires a commercial license from them. This page covers API access; for self-hosting terms, see Black Forest Labs' licensing page.

How much does the FLUX 3 Image Klein API cost?

Each image is priced by its resolution tier only. Original prices on APIMart (October 2026): 768sq $0.008, 1k $0.009, 1.5k $0.011, 2k $0.014 and 4k $0.036. Aspect ratio, the number of references, steps, seed and output_format don't change the price, and text-to-image costs the same as editing. Gold members pay 20% less and Platinum and Diamond members save up to 28%; the final charge is the completed task's cost.

How do I get a FLUX 3 Image Klein API key?

Sign up for APIMart, add credits to your balance, then create an API key on the API Keys page of the dashboard. Send it as a Bearer token with each FLUX 3 Image Klein API request; the same key works for every model on APIMart.

How do I receive images from the FLUX 3 Image Klein API?

POST /v1/images/generations returns a task_id. Query GET /v1/tasks/{task_id} until the task completes or fails, then read the image URL from data.result.images[0].url[0]. APIMart keeps results for 72 hours, so download the images you want to keep.

Is FLUX 3 Image Klein the same as FLUX.3 Klein or FLUX.2 Klein?

FLUX 3 Image Klein, FLUX 3 Klein, FLUX.3 Klein and FLUX3 Klein are names for the same model, which you call on APIMart as flux-3-image-klein. FLUX.2 [klein], released by Black Forest Labs in January 2026, is a different, earlier open-weights model and is not served by this API. Klein Base, the 50-step FLUX 3 variant for fine-tuning, is released as open weights only and has no API.

Is the FLUX 3 Image Klein API free?

No. APIMart has no free quota for the FLUX 3 Image Klein API; it is pay-as-you-go, starting at $0.008 per 768sq image at the original price, and failed tasks are refunded. If you want to run the model yourself, Black Forest Labs publishes the weights on Hugging Face under its own license.

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