bfl/flux-2/klein/4b/lora
Flux 2 Klein 4b by BFL - generate stunning images from text prompts with state-of-the-art AI. Supports multiple aspect ratios, styles, and high-resolution output for creative and commercial use.
Example output — click Run to generate your own
Send your first request
OpenAI-compatible endpoint with unified authentication and usage tracking.
https://api.sandbase.ai/v1/runbfl/flux-2/klein/4b/loraInput Schema
6 parameters · 1 required · 5 optional
| Parameter | Type | Required | Description |
|---|---|---|---|
prompt | string | Required | The prompt to generate an image from. |
seed | integer | Optional | The seed to use for the generation. If not provided, a random seed will be used. |
loras | object[] | Optional | List of LoRA weights to apply (maximum 3). · Default: [] |
aspect_ratio | string | Optional | The aspect ratio of the generated image. · Options: 21:9, 16:9, 3:2, 4:3, 5:4, 1:1, 4:5, 3:4, 2:3, 9:16 21:916:93:24:35:41:14:53:42:39:16 |
output_format | string | Optional | The format of the generated image. · Options: jpeg, png · Default: "png" jpegpng |
num_inference_steps | integer | Optional | The number of inference steps to perform. · Min: 4 · Max: 8 · Default: 4 |
Output Schema
| Field | Type | Description |
|---|---|---|
id | string | Unique identifier for the generation task |
status | string | Task status: pending, running, completed, failed, timeout |
model | string | Model used for the generation |
outputs | array | Array of output items |
outputs[].url | string | URL of the generated artifact |
outputs[].content_type | string | MIME type (e.g. image/png, video/mp4) |
error | object | null | Error details if failed, null on success |
error.type | string | Machine-readable error type code |
error.message | string | Human-readable error description |
Async Workflow
This model uses asynchronous execution. Submit a request and poll for the result.
- Submit — POST to /v1/run, receive an
id - Poll — GET /v1/run/{id} until status is
completed,failed, ortimeout - Retrieve — Read
outputsfrom the completed response
Code Examples
Ready-to-run snippets
# Step 1: Submit
curl -X POST https://api.sandbase.ai/v1/run \
-H "Content-Type: application/json" \
-H "Authorization: Bearer YOUR_API_KEY" \
-d '{
"model": "bfl/flux-2/klein/4b/lora",
"loras": [],
"prompt": "Cheetah in pre-sprint crouch, muscles tensed, gazelle visible in distance, African savanna golden grass, dust particles in air, National Geographic wildlife photography",
"output_format": "png",
"num_inference_steps": 4
}'
# Step 2: Poll result (replace <id>)
curl https://api.sandbase.ai/v1/run/<id> \
-H "Authorization: Bearer YOUR_API_KEY"API README
FLUX.2 [klein] 4B LoRA
FLUX.2 [klein] 4B LoRA combines a lightweight learned adaptation with Black Forest Labs’ smallest FLUX.2 Klein model, a compact architecture built for interactive text-to-image generation and source-aware editing. The 4B variant emphasizes accessibility and low latency while preserving photorealistic rendering, multi-reference composition, and detailed prompt understanding.
Use it for responsive design tools, local experimentation, rapid campaign variants, and high-volume image work where the 9B model’s additional capacity is unnecessary. Write detailed prompts because Klein does not depend on automatic prompt expansion; include the adapter’s learned subject or style naturally inside the complete visual brief.
Highlights
- Compact 4B visual intelligence. Runs generation and editing through the smallest Klein architecture for efficient inference.
- Interactive image creation. Produces useful visual results at latency suitable for responsive creative applications.
- Unified generation and editing. Handles prompt-only creation, source revision, and multi-reference composition in one model.
- LoRA concept specialization. Adds a learned style, subject, character, or domain while retaining Klein’s compact behavior.
Pricing
| Configuration | Billing unit | Price |
|---|---|---|
| Base generation | Per request | $0.01 |
When to Use
| ✅ Good fit | ❌ Consider alternatives |
|---|---|
| The project needs this exact generation or editing route | The intended task belongs to video, audio, or 3D media |
| Available references match every required local field | Required source assets or rights are unavailable |
| The brief can specify composition, color, and finish | Output must be deterministic at pixel level |
| Supported dimensions and formats fit final placement | Delivery requires unsupported canvas specifications |
| An asynchronous generated image fits production | A live frame-synchronous response is mandatory |
Prompt Guide
Write a complete visual brief: identify the subject and references, define composition and viewpoint, describe lighting, palette, materials, typography, and finish, then list exact preservation constraints. FLUX.2 Klein does not rely on prompt upsampling, so use clear descriptive sentences rather than sparse keywords.
{
"aspect_ratio": "21:9",
"loras": [],
"prompt": "A photorealistic editorial composition with precise subject placement, controlled lighting, exact colors, and clean typography",
"seed": 1
}
Technical Specs
| Spec | Value |
|---|---|
| Model ID | bfl/flux-2/klein/4b/lora |
| Input fields | seed (integer)<br>loras (array)<br>prompt (string)<br>aspect_ratio (string; 21:9, 16:9, 3:2, 4:3, 5:4, 1:1, 4:5, 3:4, 2:3, 9:16)<br>output_format (string; jpeg, png)<br>num_inference_steps (integer; 4–8) |
| Required input | prompt |
| Output fields | url, content_type |
| Execution | Asynchronous job |
Related Models
bfl/flux-2/klein/4b— Compare this concrete local family route.bfl/flux-2/klein/4b/base— Compare this concrete local family route.bfl/flux-2/klein/4b/base/edit— Compare this concrete local family route.