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Favicon for black-forest-labs

Black Forest Labs: FLUX.2 Klein 4B

black-forest-labs/flux.2-klein-4b

Model weights
BenchmarksCompare

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
Released
Jan 14, 2026
BenchmarksCompare
PlaygroundBenchmarksProvidersPricingPerformanceUptimeAppsActivityFAQExplore

Playground

Benchmarks

Scores on standardized evaluations and this model’s own outputs on shared benchmark prompts. Higher percentages are better — and each rank shows where this model lands among the models evaluated on that source.

Benchmark score summary for Black Forest Labs: FLUX.2 Klein 4B (Artificial Analysis and Design Arena)
SourceBenchmarkScore
Artificial AnalysisFLUX.2 [klein] 4B Elo863
Design ArenaFLUX.2 Klein 4B Models Arena Graphic Design Elo1007
Design ArenaFLUX.2 Klein 4B Models Arena Image Elo1065
Design ArenaFLUX.2 Klein 4B Models Arena Logo Elo1060

Providers

This model is hosted by one provider. OpenRouter forwards every request to it directly — no routing decisions to make.

Pricing

The average price customers actually pay for this model, next to the prices providers post. Caching and discounts mean the price actually paid is often well below the listed one.

Performance

Throughput is how fast the model writes (tokens per second — higher is better). Latency is total round-trip time (lower is better). TTFT is time-to-first-token — how long before you see anything appear (lower is better).

Uptime

Uptime is the percentage of the past 3 days that at least one provider was responding to requests. Availability is the percentage of time that inference was successfully served. OpenRouter continuously monitors and uses the next-best provider when one returns an error.

Apps

Public apps that send the most traffic to this model. Good signal for what real production workloads look like — and a hint at which use cases this model is best suited for.

Activity

Token volume and request traffic to this model over time.

API

Drop-in code to call this model. OpenRouter's API is OpenAI-compatible — most SDKs work by just swapping the base URL. The only thing that changes between models is the model slug below.

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P50, best provider

Uptime (3d)The model was reachable. Request routed to a provider.
100.00%
Availability (3d)The model returned inference from any provider. Errors and empty responses count against it.
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Availability over the last 3 days

Last 72 hours
Availability 99.37%
3 Days Ago2 Days AgoYesterdayNow

Availability over the last 24 hours

OpenRouter Availability
99.92%

When an error occurs in an upstream provider, we can recover by routing to another healthy provider, if your request filters allow it. You can access per-provider uptime data programmatically through the Endpoints API. Learn more about our load balancing and customization options.

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Frequently asked questions

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.

FLUX.2 Klein 4B costs $0.014/megapixel.

FLUX.2 Klein 4B supports the 1:1, 4:3, 3:4, 3:2, 2:3, 16:9 and 2 more aspect ratios and returns PNG and JPEG images.

FLUX.2 Klein 4B accepts text and images as input and returns images. Up to 4 reference images can be attached to one request for image editing.

FLUX.2 Max, FLUX.2 Flex, and FLUX.2 Pro are other image models from Black Forest Labs.

FLUX.2 Klein 4B was released on January 14, 2026.

More models from black-forest-labs

FLUX Video Edit

FLUX Video Edit [fast] takes a source video and an edit prompt and returns a precisely edited video. Add, remove, or replace objects and characters, rebuild the setting, edit on-screen text, change colors, materials and visual effects, change or translate dialogue with lip sync, or change the events of a clip. Output preserves the source duration, aspect ratio, and audio; inputs above 720p are downscaled to 720p. Source clips up to 15 seconds and 50 MiB.

Video$0.03/second
FLUX Video Upscale

FLUX Video Upscale is a video upscaling model from Black Forest Labs. It enlarges a single source video by 1.5× to 3× while preserving its duration, with an optional prompt and precise or creative processing modes.

Videofrom $0.075/megapixel-second
FLUX.3 Video

FLUX.3 Video is a video generation model from Black Forest Labs. It supports text-to-video, image-guided generation with opening and closing keyframes, and video continuation workflows, making it suited for controlled creative production, scene animation, and extending existing clips. It can generate synchronized audio alongside the video.

Videofrom $0.17/second
FLUX.2 Max

FLUX.2 [max] is the new top-tier image model from Black Forest Labs, pushing image quality, prompt understanding, and editing consistency to the highest level yet.

Pricing is as follows, per the docs: Input: We charge $0.03 for each megapixel on the input (i.e. reference images for editing) Output: The first generated megapixel is charged $0.07. Each subsequent megapixel is charged $0.03.

Image$0.07/megapixel
FLUX.2 Flex

FLUX.2 [flex] excels at rendering complex text, typography, and fine details, and supports multi-reference editing in the same unified architecture.

Pricing is as follows, per the docs: We charge $0.06 for each megapixel on both input and output side.

Imagefrom $0.06/megapixel
FLUX.2 Pro

A high-end image generation and editing model focused on frontier-level visual quality and reliability. It delivers strong prompt adherence, stable lighting, sharp textures, and consistent character/style reproduction across multi-reference inputs. Designed for production workloads, it balances speed and quality while supporting text-to-image and image editing up to 4 MP resolution.

Pricing is as follows, per the docs: Input: We charge $0.015 for each megapixel on the input (i.e. reference images for editing) Output: The first megapixel is charged $0.03 and then each subsequent MP will be charged $0.015.

Image$0.03/megapixel