# Flux 2 | Klein | 4B | Base | Text to Image

Flux 2 [klein] 4B from Black Forest Labs delivers text-to-image generation with enhanced realism, sharper text rendering, and integrated native editing tools.

## API Information

- **Model Slug:** flux-2-klein-4b-base-text-to-image
- **Branded URL:** https://www.eachlabs.ai/black-forest-labs/flux-2/flux-2-klein-4b-base-text-to-image
- **Provider:** Black Forest Labs
- **Category:** Text to Image
- **Output Type:** array
- **Status:** active
- **Version:** 0.0.1
- **Base Cost:** Per-megapixel pricing: $0.014 base + $0.001/extra MP (ceil rounding)
- **Estimated Processing Time:** 7 seconds
- **Last Updated:** 2026-04-27
- **Interactive Demo:** https://www.eachlabs.ai/ai-models/flux-2-klein-4b-base-text-to-image

## Pricing

- **Charge Type:** dynamic
- **Estimated Price (default example):** $0.0130
- **Pricing Details:** Per-megapixel pricing: $0.014 base + $0.001/extra MP (ceil rounding)

### Pricing Rules

| Condition | Pricing |
| --- | --- |
| Rule 1 | Per-megapixel pricing: $0.014 base + $0.001/extra MP (ceil rounding) |

## Input Schema

| Parameter | Type | Required | Default | Constraints | Description |
|-----------|------|----------|---------|-------------|-------------|
| prompt | string | Yes | - | - | The prompt to generate an image from. |
| seed | integer | No | - | - | The seed to use for the generation. If not provided, a random seed will be used. |
| num_inference_steps | integer | No | 4 | 4–8 | The number of inference steps to perform. |
| image_size | string | No | landscape_4_3 | square_hd,square,portrait_4_3,portrait_16_9,landscape_4_3,landscape_16_9 | The size of the image to generate. |
| num_images | integer | No | 1 | 1–4 | The number of images to generate. |
| enable_safety_checker | boolean | No | true | - | If set to true, the safety checker will be enabled. |
| output_format | string | No | png | jpeg,png,webp | The format of the generated image. |

## Example Request

```bash
curl -X POST https://api.eachlabs.ai/v1/prediction/ \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "flux-2-klein-4b-base-text-to-image",
  "input": {
    "prompt": "Photorealistic cityscape at dusk, modern skyscrapers with lights turning on, natural atmospheric haze, realistic reflections on glass buildings, wide-angle lens, balanced exposure, documentary-style photography, ultra-detailed, 4K realism"
  }
}'
```

## Output Schema

Response returned by `GET /v1/prediction/{id}` when the job completes:

```json
{
  "status": "success",
  "predictionID": "string",
  "output": "array",
  "metrics": {
    "predict_time": "number (seconds)"
  }
}
```

## Polling

```bash
curl https://api.eachlabs.ai/v1/prediction/{PREDICTION_ID} \
  -H "X-API-Key: YOUR_API_KEY"
```

| Status | Meaning |
|--------|---------|
| `processing` | Still running — poll again |
| `success` | Done — read `output` |
| `error` | Failed — read `message` / `details` |

## Webhook (alternative to polling)

Pass `"webhook_url": "https://your.host/path"` in the create request. Eachlabs POSTs this payload when the job ends:

```json
{
  "exec_id": "prediction-uuid",
  "status": "succeeded",
  "output": "https://...",
  "error": ""
}
```

`status` is `"succeeded"` or `"failed"`. `exec_id` equals the `predictionID` from create. Return 2xx within 30 seconds.

## Errors

Error body: `{ "status": "error", "message": "...", "details": "..." }`

| Code | Meaning |
|------|---------|
| `400` | Invalid input |
| `401` | Missing / invalid `X-API-Key` |
| `404` | Unknown model or prediction id |
| `429` | Rate limit — 100 creates / min, 10 concurrent per key |
| `5xx` | Retry with backoff |

## Overview

**flux-2-klein-4b-base-text-to-image — Text-to-Image AI Model**

flux-2-klein-4b-base-text-to-image, the 4B Base model from Black Forest Labs' FLUX.2 [klein] family, empowers developers and creators with high-quality text-to-image generation that runs efficiently on consumer GPUs under 12GB VRAM. This base version delivers full control through 25-50 inference steps, enabling precise customization for professional workflows like rapid prototyping and detailed image creation. Unlike distilled variants, it prioritizes flexibility for fine-tuning while supporting text-to-image and integrated editing, making it ideal for **Black Forest Labs text-to-image** applications in ComfyUI and beyond.

## Usage Notes

- API Base URL: `https://api.eachlabs.ai/v1`
- Authentication: send `X-API-Key: YOUR_API_KEY`. Generate a key from the Eachlabs dashboard at https://www.eachlabs.ai/dashboard/api-keys.
- File-typed parameters (`*_url`, `image_url`, `video_url`, `audio_url`, etc.) accept publicly-reachable HTTPS URLs only. Upload your asset first (GCS / S3 / your CDN) and pass the resulting URL. Data-URIs and localhost URLs are rejected.
- For structured parameters (arrays / objects) send real JSON values, not stringified payloads.
- Monetary values are reported in USD; per-token / per-megapixel rates may be billed in micro-cents internally.
- Prefer `webhook_url` over polling for long-running predictions — see the Webhook Callback section.