FLUX (Black Forest Labs)

Black Forest Labs' FLUX family: open-weight FLUX.1 and FLUX.2 image models plus FLUX 3, an API video model making 20-second clips with native audio.

Last reviewed September 6, 2026 Pay-as-you-go (API) / Free (Open Weights)

At a glance

FLUX is Black Forest Labs’ model family, and it has moved a long way from the three image checkpoints that made its name in 2024. Today it spans three generations: FLUX.1, whose [dev] and [schnell] weights are still the most-downloaded open image models BFL publishes; FLUX.2, the current image line, with an open 32B checkpoint and a 4B one small enough for a laptop GPU; and FLUX 3, a multimodal model whose first shipped capability is 20-second video with native audio.

Overview

Black Forest Labs — founded by members of the team behind the original Stable Diffusion — released FLUX.1 in August 2024 in three variants: [pro] via API, [dev] as open weights for non-commercial use, and [schnell] as an Apache 2.0 four-step distillation. Its text rendering and prompt adherence were a visible step past what open image models could do at the time, and a very large LoRA ecosystem grew on the [dev] weights.

Two full generations have shipped since:

• FLUX.2 (25 November 2025) replaced FLUX.1 as the image line. It pairs a Mistral-3 24B vision-language model with a rectified flow transformer, edits at up to 4 megapixels, and can hold consistency across up to ten reference images at once. [pro], [flex] and the open 32B [dev] launched together; [max] followed on 16 December 2025, and the small, fast [klein] models on 15 January 2026.
• FLUX 3 was announced on 23 July 2026 as a single model jointly trained on image, video and audio rather than three models behind a shared API. Video shipped first — preview 4 August 2026, generally available 5 August. Image generation was promised “in the coming weeks” and, as of 6 September 2026, has not opened; neither has the planned open-weight FLUX 3 [dev].

One deprecation matters if you have old code: the original FLUX Pro 1.0 endpoints and the finetuning API were switched off on 31 October 2025. FLUX 1.1 [pro] and FLUX.1 Kontext [pro] / [max] are still served.

Key Features

• Video with native audio: FLUX 3 generates up to 20 seconds at HD or Full HD (1920×1088 for 16:9), 24 fps, with synchronised dialogue, sound effects and ambience, and lip-sync in more than 14 languages. Text-to-video, image-to-video, keyframes and video continuation are all supported, including several scenes and camera angles inside one clip.
• Text rendering that survives: rendering legible typography inside an image was FLUX.1’s original headline, and FLUX.2 [flex] is tuned specifically for it — infographics, UI mockups and packaging with fine text. FLUX 3 carries the same ability into moving footage.
• Multi-reference editing: FLUX.2 accepts up to ten reference images in a single request to keep a character, product or style consistent across a set.
• Open weights at four sizes: 4B, 9B, 12B and 32B, so the same family covers a 12GB laptop GPU and a 64GB checkpoint on a workstation.
• In-context editing (Kontext): FLUX.1 Kontext [pro] / [max] (May 2025) and [dev] (June 2025) edit an image from an instruction while preserving the rest of the frame.
• A wide tool endpoint set: beyond the original FLUX.1 Tools — Fill, Depth, Canny and Redux (21 November 2024) — BFL shipped Outpainting (14 May 2026), Erase (21 May), Virtual Try-On (28 May, v2 on 17 July), Deblur (25 June) and Video Upscale to 2K/4K (20 August 2026).
• Agent-native access: an official MCP server (11 May 2026, video support added 11 August) plus published agent skills let Claude Code, Cursor and Windsurf drive generations directly.

How It Works

Every FLUX image model is a rectified flow transformer: instead of the many-step denoising schedule of a classic diffusion model, it learns a straighter path from noise to image, which is what makes few-step distillations practical. FLUX.1 [schnell] produces usable output in four steps; FLUX.2 [klein] gets to sub-second inference on consumer hardware.

FLUX.2 changed the text side. Rather than the frozen CLIP/T5 encoders of the FLUX.1 era, it conditions on a Mistral-3 24B vision-language model, which is where the multi-reference editing and the improved instruction-following come from — the model reads reference images the same way it reads the prompt.

FLUX 3 goes further and drops the separation between modalities. BFL calls the underlying method Self-Flow, publicised in March 2026: one architecture trained jointly on images, video and audio, so speech, effects and picture are generated together rather than dubbed onto a silent clip afterwards. The same backbone is what BFL and its partner mimic use for video-action prediction in robotics. On BFL’s own reported Elo evaluation, FLUX 3 leads text-to-video and image-to-video against Seedance 2.0, MiniMax H3 and Gemini Omni Flash — a vendor-run comparison, so treat it as a claim rather than an independent result.

Practically, FLUX 3 exposes a draft mode: a cheap, fast render for iterating on prompt and blocking, then a full render once the shot is right.

Technical Details

Sizes are the single-file checkpoint on Hugging Face; the full repos, which also carry sharded diffusers weights and text encoders, are roughly 58 GB for the FLUX.1 models and 178 GB for FLUX.2 [dev]. FP8 and NVFP4 quantizations are published for [klein], FLUX.2 [dev] and FLUX.1 [dev], and a 4-bit build (diffusers/FLUX.2-dev-bnb-4bit) is what makes the 32B model fit an RTX 4090 or 5090.

The licence split is the part to read carefully, because it is not consistent across the family: only FLUX.1 [schnell] and FLUX.2 [klein] 4B are Apache 2.0. Everything else with downloadable weights — [dev] at both generations, Kontext [dev], Krea [dev], [klein] 9B — is FLUX Non-Commercial, which means a paid licence from BFL before you sell anything made with it.

Use Cases

Design and marketing

• Typographic work: posters, packaging, UI mockups and infographics where the text has to be spelled correctly — FLUX.2 [flex] is the variant tuned for this.
• Product photography: a product shot placed into new lighting and environments, with multi-reference editing keeping the object identical across a campaign.
• Brand consistency: LoRAs fine-tuned on the [dev] weights for a house style, character or catalogue.

Video and motion

• Short-form social: a 20-second clip with dialogue and ambience generated in one pass, rather than assembled from a silent generation plus a separate TTS track.
• Previsualisation: draft mode for blocking a shot cheaply before committing to a full render.
• Multilingual variants: the same scene with lip-synced dialogue in a different language.

Local and embedded

• On-device generation: [klein] 4B runs on consumer laptops; ASUS ProArt machines shipped with local Klein support in June 2026.
• Self-hosted pipelines: ComfyUI graphs on your own GPUs, where data cannot leave the building.

Integrations

• BFL API at api.bfl.ai — the direct route, and the only one for FLUX 3 video. The older api.bfl.ml host is documentation only.
• ComfyUI — first-class support for every open FLUX generation, with ControlNet and node-based chaining.
• Diffusers — black-forest-labs/FLUX.1-dev, FLUX.2-dev, FLUX.2-klein-4B and the rest load directly in the Hugging Face pipeline.
• Hosted APIs — fal.ai and Replicate carry the open and several proprietary variants; Leonardo.ai and other platforms expose FLUX inside their own editors.
• MCP server and agent skills — generate and enhance images and video from Claude Code, Cursor or Windsurf without writing an API client.

Pricing & Access

Black Forest Labs bills per megapixel for images and per second for video, prepaid in credits (1 credit = $0.01). These are BFL’s own rates from bfl.ai/pricing; a third-party host’s price is its own, not the vendor’s.

Images, per megapixel (from):

• FLUX.2 [klein] 4B — $0.014
• FLUX.2 [klein] 9B — $0.015
• FLUX.2 [pro] — $0.03 generation, $0.045 editing
• FLUX.2 [flex] — $0.05
• FLUX.2 [max] — $0.07
• FLUX 1.1 [pro] — $0.04 per image ($0.06 Ultra or Raw); FLUX.1 Kontext [pro] $0.04, [max] $0.08; FLUX.1 Fill [pro] $0.05

FLUX 3 video, per second of output:

• Text-to-video and image-to-video — $0.17/s HD, $0.29/s Full HD; draft mode $0.06/s
• Video continuation — $0.43/s HD, $0.54/s Full HD; draft $0.12/s
• Video Upscale — $0.07 per megapixel-second precise, $0.10 creative

A five-second HD clip therefore costs about $0.85, and the same clip in draft about $0.30.

Open weights are free to run on your own hardware, subject to the licence table above. Hosted rates differ: fal.ai charges $0.025 per megapixel for FLUX.1 [dev] and $0.003 for [schnell].

Getting Started

Option A: The BFL API

import os, requests, time

r = requests.post(
    "https://api.bfl.ai/v1/flux-2-pro",
    headers={"x-key": os.environ["BFL_API_KEY"]},
    json={
        "prompt": "A neon sign reading 'OPEN 24/7' in a rainy Tokyo alley, f/1.8",
        "aspect_ratio": "3:2",
    },
).json()

while True:
    result = requests.get(r["polling_url"], headers={"x-key": os.environ["BFL_API_KEY"]}).json()
    if result["status"] == "Ready":
        print(result["result"]["sample"])
        break
    time.sleep(1)

Note the polling status string: it is Ready, not SUCCESS, since the webhook payload change of 17 February 2026.

Option B: Local, in ComfyUI

1. Install ComfyUI.
2. Pick a checkpoint for your GPU. 12GB and under: FLUX.2-klein-4B (7.8 GB, Apache 2.0). 24GB: FLUX.1-dev (23.8 GB) or FLUX.2-klein-9B. Workstation: FLUX.2-dev, 4-bit quantized.
3. Place the file in ComfyUI/models/unet/, or let ComfyUI Manager fetch it.
4. Load a FLUX workflow and generate.

Option C: Hosted, no setup

• fal.ai — fal.ai/models/fal-ai/flux, web UI plus API.
• Replicate — replicate.com/black-forest-labs.
• Hugging Face Spaces — the free FLUX.1 [schnell] demo.

Prompting notes

• Put text you want rendered in quotes, verbatim: "OPEN 24/7".
• Describe lighting and optics — “golden hour”, “f/1.8 bokeh”, “35mm” — rather than piling on style adjectives.
• Iterate on [schnell] or [klein] 4B, then re-run the winning prompt on [dev] or [pro].
• For video, draft mode first. A 20-second Full HD full render is roughly twenty times the price of the draft.

Limitations

• The licence, not the download, is the constraint. Four of the six open checkpoints are non-commercial. Teams have shipped on FLUX.1 [dev] without noticing; that requires a paid BFL licence.
• FLUX 3 is API-only. No weights, no self-hosting, no offline use, and the promised FLUX 3 [dev] backbone has no ship date.
• FLUX 3 Image has not shipped. Announced 23 July 2026 as coming “in the coming weeks”; still early access on 6 September 2026. For images the current answer is FLUX.2.
• FLUX.2 [dev] is heavy. 32B parameters, a 64.4 GB checkpoint, and realistically 4-bit quantization to fit a single consumer card — with the quality cost that implies.
• Video continuation is capped shorter than generation. Since 17 August 2026 continuation requests max out at 15 seconds, against 20 for the other modes.
• The ecosystem lags the frontier. The community LoRAs, ControlNets and workflows are overwhelmingly built for FLUX.1 [dev], not FLUX.2 — part of why the older weights still out-download the newer ones.
• No free tier. BFL is prepaid credits only; the free route is running open weights yourself.

Alternatives

• Midjourney — stronger default aesthetics, closed, no self-hosting.
• Qwen-Image 3.0 and Z-Image — open-weight image models that compete directly with FLUX.2 [dev], the latter at a fraction of the parameter count.
• HunyuanImage 3.0 and HiDream-O1-Image — other large open image models.
• Stable Diffusion 3.5 — lighter, older, and still the default for a lot of local tooling.
• Seedream 5.0 and Nano Banana — closed image models at the current quality frontier.
• For video: Veo 3.1, Kling 3.0, Seedance 2.5, MiniMax H3, Vidu Q3 Pro, or Wan 3.0.

Community & Support

• Black Forest Labs: bfl.ai — blog, model announcements and pricing.
• Documentation: docs.bfl.ml — endpoints, pricing table and release notes.
• Hugging Face: huggingface.co/black-forest-labs — 35 repos including every open checkpoint and its quantizations.
• GitHub: github.com/black-forest-labs/flux — reference inference code.
• Civitai: civitai.com — the community LoRA library, still mostly FLUX.1-based.
• Reddit: r/StableDiffusion — workflows and troubleshooting.

Related Tools

• Midjourney
• Ideogram
• Stable Diffusion
• ComfyUI
• Leonardo.ai
• Runway