FLUX.2 Klein Base 4B LoRA API

About FLUX.2 Klein Base 4B LoRA

FLUX.2 Klein Base 4B LoRA runs Black Forest Labs' FLUX.2 [klein] Base 4B, the undistilled 4-billion-parameter foundation model released under Apache 2.0 on 15 January 2026, with up to three of your own LoRA files per request. It is the build its makers recommend for fine-tuning and LoRA training: slower than the distilled 4B, with more varied results and stronger response to style LoRAs. Text to image and editing, with nothing filtered.

Call it with the model name black-forest-labs/flux-2-klein-base-4b-lora/text-to-image on POST /jobs/createTask, from 3 credits per image ($0.03). New accounts get 30 free credits to try it in the Playground first.

Introduction

FLUX.2 Klein Base 4B LoRA Text to image makes one image from a written prompt on Black Forest Labs' FLUX.2 [klein] Base 4B, the undistilled 4-billion-parameter foundation model released under Apache 2.0, with up to three of your own LoRA files loaded. Nothing is filtered.

Choose a mode by starting material

Key features

The build LoRAs are trained on

Black Forest Labs recommends Base 4B for fine-tuning and LoRA training. LoRAs trained on it apply here at full strength, and in our tests LoRAs trained on the distilled 4B applied too.

Strong style response

Style LoRAs show strongly on this build: in our tests the same anime LoRA at scale 2 redrew a photographic scene in its style on Base, while the distilled 4B changed only slightly.

More variety, more time

The undistilled model gives more varied results between seeds and took about 20 seconds per image in our tests, around four times the distilled 4B.

Request parameters

Pricing

Prices are in credits, the same credits you use on the website (1 credit = $0.01). The hold is taken when the task is accepted and settled to the actual charge when it finishes; failed tasks are refunded.

Each task is rounded up to whole credits, so one run at the lowest tier costs 3 credits per image ($0.03).

For an exact number before you run, send the same body to POST /jobs/quote.

Use cases

Checking a LoRA you trained

Run your Base 4B LoRA at a few scales and seeds without setting up a GPU, compare each result with a run that has no LoRA, and ship the same file to production once it holds up.

Painted and pixel-art series

Painting, colored-pencil and pixel-art LoRAs keep a whole series in one look across nine aspect ratios, from square thumbnails to 21:9 banners and 9:16 phone frames.

Exploring compositions

Use the extra variety between seeds to find a layout you like, then keep that seed and refine the clothing, light and setting around it one sentence at a time.

Prompt guide & pro tips

Trigger first, then full sentences

Start with the trigger phrase from the LoRA page, then describe subject, clothing, place and light.

Begin at scale 1

Styles show strongly here. Lower to 0.5 for a lighter touch; at 4 the image turned to noise in our test.

Compare against no LoRA

Run the same prompt and seed without the LoRA. If the two results look the same, the file was made for another base model, such as FLUX.1 or the 9B Klein models: those load without an error and do nothing here.

Keep signs out of the frame

Signs, labels and chart headings often come out as garbled text. Describe them as blank or leave them out.

Use direct, public links

The link must download the .safetensors file itself.

API quick start

Call the FLUX.2 Klein Base 4B LoRA API in three steps

1. Create an API key. Sign in to PopNow and create a key in the API console. Keys start with sk-popnow- and use the same credits as the website.
2. Send the request. POST /jobs/createTask with model black-forest-labs/flux-2-klein-base-4b-lora/text-to-image and an input object that follows the parameter table. The response returns a task ID straight away.
3. Get the result. Poll GET /jobs/recordInfo with the task ID, or pass a callBackUrl and we post the result to it. Download the output links when the task succeeds.

# 1. Create the task. Keep the Idempotency-Key if you retry after a network error.
export IDEMPOTENCY_KEY="$(uuidgen)"
curl -X POST https://api.popnow.ai/api/v1/jobs/createTask \
  -H "Authorization: Bearer $POPNOW_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $IDEMPOTENCY_KEY" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-base-4b-lora/text-to-image",
  "input": {
    "prompt": "A ceramic teapot on a linen cloth, soft window light, muted palette",
    "aspect_ratio": "1:1",
    "resolution": "1k"
  }
}'

# 2. Copy data.taskId from the response, then poll until state is succeeded, failed, canceled or expired.
TASK_ID="TASK_ID_FROM_RESPONSE"
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$TASK_ID" \
  -H "Authorization: Bearer $POPNOW_API_KEY"

Replace the prompt and any links with your own. The API tab has the response, polling and callback reference.

FLUX.2 Klein Base 4B LoRA API questions

All FLUX models

FLUX.2 Klein 4B LoRA is about four times faster and follows edit instructions more reliably.

• FLUX.2 Max APITop-tier FLUX: photoreal light and exact brand colorsFrom 11 credits per image
• FLUX 3 APIVideo with synced sound and a quick draft tierFrom 45 credits for a 5-second clip
• FLUX.2 Klein 9B LoRA APIFast FLUX.2 Klein 9B that loads up to three of your LoRAsFrom 3 credits per image
• FLUX.2 Klein Base 9B LoRA APIUndistilled Klein 9B for varied looks with your LoRAsFrom 4 credits per image
• FLUX.2 Klein 4B LoRA APISmall, quick FLUX.2 Klein 4B with your own LoRAsFrom 3 credits per image
• FLUX.2 Klein Base 4B LoRA APIUndistilled Klein 4B that loads your own LoRAsFrom 3 credits per image
• FLUX.2 Klein 9B APIFast FLUX edits that keep faces and poses intactFrom 2 credits per image
• FLUX.2 Klein 4B APIThe smallest, quickest FLUX for rapid draftsFrom 2 credits per image
• FLUX.2 Dev LoRA APIFLUX.2 Dev images and edits with your own LoRAsFrom 4 credits per image
• FLUX.2 Pro APIPhotoreal images with readable text and hex color controlFrom 5 credits per image
• FLUX.2 Flex APISpells headlines and labels exactly as writtenFrom 9 credits per image
• FLUX.2 Dev APIOpen-weights FLUX that can merge people into one sceneFrom 2 credits per image
• FLUX.1 Krea Dev LoRA APIPhotographic FLUX.1 Krea with your own LoRAsFrom 4 credits per image
• FLUX.1 Dev ControlNet LoRA APIPose, depth or edge control on FLUX.1 with your LoRAsFrom 6 credits per image
• FLUX.1 Fill Dev LoRA APIMasked inpainting on FLUX.1 Fill with your own LoRAsFrom 7 credits per image
• FLUX.1 Dev LoRA APIClassic FLUX.1 Dev with up to three of your LoRAsFrom 3 credits per image
• FLUX.1 Schnell LoRA APIFast FLUX.1 Schnell that loads your own LoRAsFrom 1 credit per image

Other image APIs

• Qwen Image 2.1 LoRA APIQwen Image 2.1 images and edits with up to three of your LoRAsFrom 5 credits per image
• MiniMax H3 Image LoRA APIH3 stills and edits with up to three of your LoRAsFrom 7 credits per image
• Anima Turbo LoRA APIAnime art with your own style or character LoRAsFrom 3 credits per image
• Krea 2 Turbo LoRA APIKrea 2 Turbo images and restyles with your own LoRAsFrom 4 credits per image
• P-Image LoRA APIFast P-Image renders and edits with one LoRA of your ownFrom 1 credit per image
• Z-Image Base LoRA APIZ-Image Base with up to three of your own LoRAsFrom 3 credits per image

More about FLUX.2 Klein Base 4B LoRA

Try it

FLUX.2 Klein Base 4B LoRA AI Image Generator onlineCreate images with FLUX.2 Klein Base 4B LoRA in PopNow

Docs

FLUX.2 Klein Base 4B LoRA model ID and input schema in the API docsPopNow API quickstart: your first request in five minutesImage generation guide for the PopNow APIWebhooks: get FLUX.2 Klein Base 4B LoRA results without polling