# FLUX 3 Image Klein API (Black Forest Labs)

> FLUX 3 Image Klein is Black Forest Labs' compact 5.6B open-weights FLUX 3 Image model: fast 16-step text-to-image in 15 aspect ratios up to 4K, and editing with up to 10 reference images.

Page: https://cheapergen.com/models/bfl/flux-3-image-klein · API reference: https://cheapergen.com/models/bfl/flux-3-image-klein/api · Live status and uptime: https://cheapergen.com/models/bfl/flux-3-image-klein/status

## Pricing
Official list price source: 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.

| Tier | Official | CheaperGen | Save |
|---|---|---|---|
| 768 | $0.0080/image | $0.0011/image | 87% |
| 1K | $0.0090/image | $0.0019/image | 79% |
| 1.5K | $0.0110/image | $0.0043/image | 61% |
| 2K | $0.0140/image | $0.0074/image | 48% |
| 4K | $0.0360/image | $0.0342/image | 5% |
| Edit 1K | $0.0090/image | $0.0085/image | 6% |
| Edit 2K | $0.0140/image | $0.0133/image | 5% |
| Edit 4K | $0.0360/image | $0.0342/image | 5% |

## Specs
- Resolutions: 768 · 1K · 1.5K · 2K · 4K (edits: 1K · 2K · 4K)
- Aspect ratios: 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 (4K and edits: 1:1 · 4:3 · 3:4 · 3:2 · 2:3 · 16:9 · 9:16 · 21:9 · 9:21)
- Edit inputs: Up to 10 images
- Model: 5.6B, distilled (16 steps)
- Prompt upsampling: Not included — write full scene descriptions
- Weights: Open (FLUX Kommunity License)
- Enable Safety Checker: Default true · can be set to false over the API

## Endpoints

### Text to Image — `POST https://cheapergen.com/api/v1/run/bfl/flux-3-image-klein/text-to-image`

| Param | Type | Required | Description |
|---|---|---|---|
| prompt | string | yes | Describe the shot: subject, action, camera movement, lighting and style. |
| aspect_ratio | string (enum) (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) | no | Output image shape. |
| resolution | string (enum) (768, 1K, 1.5K, 2K, 4K) | no | 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. |
| seed | integer | no | Use the same seed and settings to reproduce a result. Leave empty for random. |
| enable_safety_checker | boolean | no | If set to true, the safety checker will be enabled. Content our Acceptable Use Policy prohibits stays blocked either way. |

```bash
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"
}'
```

### Image Edit — `POST https://cheapergen.com/api/v1/run/bfl/flux-3-image-klein/edit`

| Param | Type | Required | Description |
|---|---|---|---|
| prompt | string | yes | Describe the shot: subject, action, camera movement, lighting and style. |
| image_urls | string[] (URLs) | yes | Up to 10 reference images to edit or combine. Refer to them as "image 1", "image 2"… in the prompt. |
| aspect_ratio | string (enum) (auto, 1:1, 4:3, 3:4, 3:2, 2:3, 16:9, 9:16, 21:9, 9:21) | no | Output image shape. |
| resolution | string (enum) (1K, 2K, 4K) | no | Output size tier: 1K ≈ 1 MP, 2K ≈ 4 MP, 4K ≈ 16 MP. |
| seed | integer | no | Use the same seed and settings to reproduce a result. Leave empty for random. |
| enable_safety_checker | boolean | no | If set to true, the safety checker will be enabled. Content our Acceptable Use Policy prohibits stays blocked either way. |

```bash
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"
}'
```

## Getting the result
Jobs are async. Poll `GET https://cheapergen.com/api/v1/generations/{id}` until status is succeeded/failed/canceled, or pass `webhook_url`. Failed generations are refunded automatically.

## FAQ
**How is FLUX 3 Image Klein priced?**
Per image by resolution tier — 768, 1K, 1.5K, 2K or 4K — like Black Forest Labs' own API, and below BFL's price at every tier: a fraction of a cent at 768 and 1K. Edits have their own price per output size (1K, 2K or 4K), the same whatever the number of references. Failed generations are not charged.

**Is this Black Forest Labs' FLUX 3 Image Klein?**
Yes: BFL's own open weights — the distilled 16-step checkpoint that BFL's API also serves — served on optimized GPU inference for open-source models. One difference: BFL's API first rewrites your prompt with Klein's prompt upsampler; here the prompt reaches the model as written, so describe the full scene.

**Can it edit images or render 4K?**
Yes. Image Edit takes 1–10 reference images — refer to them as image 1, image 2… in the prompt — at 1K, 2K or 4K, and text-to-image goes up to 4K. Both are priced below BFL's own API.

**Can I use the output commercially?**
Black Forest Labs releases Klein under the FLUX Kommunity License, which sets the terms for commercial use (free for businesses below the revenue limit in the license; larger businesses need a commercial license from BFL). Check it and our Terms of Service before commercial use.

FLUX 3 Image Klein is Black Forest Labs' open-weights model. CheaperGen provides API access to the open weights, run on GPU inference for open-source models, and does not own the model.