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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

Example outputs summary for Black Forest Labs: FLUX.2 Klein 4B

  • Text to Image: Editorial architectural photograph of a contemporary neighborhood storefront at blue hour, glowing warmly against the dusk. Above the entrance, a warm-white neon sign in flowing hand-bent cursive reads exactly "OpenRouter", the only text in the scene. Large windows reveal a cozy, lived-in interior: wood shelves styled with books and ceramics, lush trailing plants, and soft pendant lighting. Potted plants and a bicycle rest by the entrance, and golden light spills across the wet pavement in gentle reflections. Straight-on composition, realistic materials, quiet street with no people. — generated with Black Forest Labs: FLUX.2 Klein 4B

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 Elo838
Design ArenaFLUX.2 Klein 4B Models Arena Graphic Design Elo1004
Design ArenaFLUX.2 Klein 4B Models Arena Image Elo1059
Design ArenaFLUX.2 Klein 4B Models Arena Logo Elo1060

Benchmark outputs summary for Black Forest Labs: FLUX.2 Klein 4B

  • Full wine glass: A wine glass filled to the brim with white wine, the surface level with the rim of the glass, standing upright on a plain wooden table. Straight-on eye-level shot, glass upright and not tilted, no other objects in the frame. (Tied 10th of 60 on this prompt)
  • Closed umbrellas: Wide street-level photograph of about twelve people crossing a city street in heavy rain. Every person is carrying a closed, furled umbrella held down at their side. Not a single umbrella is open. Each umbrella is clearly visible. They are all getting soaked. No other people in the frame. (Tied 34th of 60 on this prompt)
  • Three fingers: Close straight-on photograph of an open right hand raised palm towards the camera, with exactly three fingers extended straight up and the other two folded down into the palm. Plain background, nothing else in the frame. (Tied 33rd of 60 on this prompt)
  • Cards & dice: Exactly four playing cards face up in a single straight row on a polished marble counter, evenly spaced, all the same size, showing the seven of hearts, the eight of spades, the nine of diamonds and the ten of clubs from left to right. No other objects in the frame. Straight-on eye-level shot, soft even light. (52nd of 60 on this prompt)
  • Long exact string: A white A4 poster on a brick wall reading exactly "SPRING CLEARANCE - EVERYTHING 40% OFF - SATURDAY 14 JUNE, 9AM TO 6PM". No other text in the frame. (Tied 29th of 60 on this prompt)
  • Multiple languages: Straight-on photograph of a white overhead directional sign in an international airport terminal, with a black arrow pointing right at the left end. The sign carries the same word in four scripts on four stacked lines, in this order from top to bottom: "DEPARTURES", then the Japanese 出発, then the Korean 출발, then the Arabic المغادرة. Clean sans-serif lettering, sharp focus, no other text anywhere in the frame. (Tied 50th of 60 on this prompt)
  • Occlusion: Straight-on eye-level photograph of a plain wooden desk. On the left, a closed hardcover book with a dark red cover stands upright, its front cover facing the camera. A blue ceramic mug stands on the desk to the right of the book and clearly further back, about 20 cm behind it, positioned so that the right edge of the book overlaps and hides the left third of the mug. The mug's handle points to the right and the whole rim of the mug is visible. Bare desk surface is visible between the book and the mug. Nothing else on the desk. Plain wall behind, soft even light. (Tied 39th of 60 on this prompt)
  • Mirror: Straight-on eye-level photograph of a bathroom vanity. A large rectangular mirror covers the wall behind the counter and its bottom edge meets the countertop, so both the objects and their reflections are visible. On the counter, a tall red toothbrush cup on the left and a tall green glass bottle on the right, both roughly 20 cm tall and well apart from each other. The mirror reflects the counter and the objects on it accurately. Nothing else in the frame. (Tied 2nd of 60 on this prompt)
  • Plain zebra: Photograph of a zebra standing side-on in short grass. Its coat is a uniform solid grey with no stripes, no bands and no markings of any kind anywhere on its body. The whole animal is visible. Sharp focus. (Tied 27th of 60 on this prompt)
  • Times Square: Wide street-level photograph of Times Square in New York at night, wet asphalt reflecting the lights. Every billboard, screen, storefront window, awning, taxi door and road marking is completely blank — lit with plain colour fields and soft gradients only. No letters, no words, no numbers, no logos, no lettering of any kind anywhere in the frame. Sharp focus, straight-on shot. (Tied 11th of 60 on this prompt)
  • Minimal diff: From the reference photo, change only the sign text to "ROUTE 7 ESPRESSO - OPEN TILL 8". Keep the sign, wall, lighting and framing identical. (Tied 5th of 60 on this prompt)
  • Object removal: Remove only the second cup from the left in the reference photo. Leave the other four cups exactly as they are, in the same positions, and leave the shelf, towel, wall, plant and lighting untouched. (Tied 23rd of 60 on this prompt)
  • Person removal: In the reference photo, remove only the person in the yellow coat. Their shadow on the pavement and their reflection in the shop window must be removed as well. Reconstruct the pavement and the window glass behind them. The person in the red coat and the person in the green coat must stay completely unchanged, including their own shadows and their own reflections. Change nothing else in the frame. (Tied 45th of 60 on this prompt)
  • Product placement: Product photograph of the ceramic mug from the reference image, standing upright on a café table. Show the same side of the mug, from the same side-on eye-level angle as the reference, with the handle on the right. The shape, proportions, colours, moulded relief and every painted detail must match the reference exactly. Only the setting and lighting change: soft daylight in a café interior, shallow depth of field. (Tied 1st of 60 on this prompt)
  • Four references: Place the person from the portrait reference at the desk in the scene reference, wearing the rust orange canvas jacket from its reference and holding the navy blue travel mug from its reference in one hand. Keep the face, the jacket and the mug exactly as they appear in the references — same colours, same details, same proportions. Do not change the room. (Tied 41st of 60 on this prompt)
  • Portraits: Studio headshot of a woman in a charcoal blazer against a mid-grey seamless backdrop, lit by a large softbox slightly above and to the left with a soft fill from the right, catchlights in both eyes. An 85mm look with shallow depth of field, skin texture and flyaway hairs kept rather than smoothed.
  • People in scenes: Photograph of four cooks working the pass in a restaurant kitchen at service, plating three dishes at once, several hands in frame and some of them overlapping. One cook partly hidden behind another, steam rising into hard overhead light, each face clearly a different person.
  • Animals: Photograph of a tabby cat asleep on a sunlit windowsill, fur lit from behind so the individual hairs glow at the edges, one ear turned toward the camera. Shallow depth of field, a houseplant soft in the background, quiet morning light.
  • Landscape and nature: Photograph of an old-growth temperate rainforest after rain, moss on every trunk and fallen log, ferns dense across the floor, thin fog between the far trees. Overcast light with no direct sun, everything from the nearest fern to the last trunk in focus.

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.

Not currently available through EU in-region routing. In-region routing docs

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Uptime (3d)The model was reachable. Request routed to a provider.
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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

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Availability over the last 24 hours

OpenRouter Availability
99.93%

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 provider routing 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 3 Image Klein, FLUX 3 Image, FLUX.2 Max and 2 more 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 3 Image Klein

FLUX 3 Image Klein is an open-weights image generation and editing model from Black Forest Labs. It is suited for text-to-image, multi-reference editing that keeps characters and subjects consistent across images, reference-based style transfer, and text rendering. At 5.6B parameters, it is the smaller, faster member of the FLUX 3 Image family.

Imagefrom $0.008/image
FLUX 3 Image

FLUX.3 Image is Black Forest Labs' flagship image generation and editing model. It handles text-to-image and multi-reference editing with up to 10 input images, and renders at fixed resolution tiers from 768 up to 4K with a selectable aspect ratio. Pricing is a flat per-image rate that scales with the chosen resolution tier.

Imagefrom $0.041/image
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 $0.035/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