FLUX.2 [klein] 4B is the fastest and most cost-effective model in the FLUX.2 family, optimized for high-throughput use cases while maintaining excellent image quality.
Pricing is based on the output image. The first generated megapixel is charged $0.014. Each subsequent megapixel is charged $0.001.
Modalities
Price
$0.014/megapixel
Context
41K
Weekly Tokens
381M
Released
Jan 14, 2026
Create an API key from your OpenRouter dashboard and set it as an environment variable:
Use black-forest-labs/flux.2-klein-4b with the OpenRouter API:
OpenRouter supports image generation models that only output images and not text. These models can create images from text prompts when you specify modalities: ["image"] in your request. The generated images are returned as base64-encoded data URLs in the assistant message. Learn more about image generation.
In the examples below, the OpenRouter-specific headers are optional. Setting them allows your app to appear on the OpenRouter leaderboards.
For information about using third-party SDKs and frameworks with OpenRouter, please see our frameworks documentation.
Add "stream": true to your request body to receive responses as server-sent events:
Sends a request for a model response for the given chat conversation. Supports both streaming and non-streaming modes.
https://openrouter.ai/api/v1/chat/completionsBearer $OPENROUTER_API_KEYapplication/jsonoptional — your site URL, for rankingsoptional — your site name, for rankingsblack-forest-labs/flux.2-klein-4bCreates a streaming or non-streaming response using the OpenAI Responses API format.
Docshttps://openrouter.ai/api/v1/responsesBearer $OPENROUTER_API_KEYapplication/jsonoptional — your site URL, for rankingsoptional — your site name, for rankingsblack-forest-labs/flux.2-klein-4b| Name | Type | Default | Description |
|---|---|---|---|
seed | integer | — | If specified, the inferencing will sample deterministically, such that repeated requests with the same seed and parameters should return the same result. |