For FLUX models, which variants use true CFG and negative prompts, and which are guidance-distilled with a scalar guidance_scale?

Problem. Negative prompts written for SD models are carried over to FLUX. Conditions. diffusers FluxPipeline family. Source statements. FLUX.1-schnell is timestep-distilled: guidance_scale needs to be 0, it benefits from fewer steps and max_sequence_length cannot exceed 256. FLUX.1-dev is guidance-distilled: it takes about 50 steps and the docs use guidance_scale=3.5. Fill and control variants (Canny, Depth, Fill) are also guidance-distilled; the docs use guidance_scale=30.0 for Canny, 10.0 for Depth. One diffusers example for FLUX.1-dev with an IP-Adapter passes negative_prompt='' together with true_cfg_scale=4.0, showing that FluxPipeline exposes a separate true CFG path. BFL's CLI example for Kontext uses --guidance 2.5 (C3-B576-16). Method (inference). Treat the scalar guidance_scale on dev as a distilled 'fake CFG' that is not driven by a negative prompt; to use a negative prompt on FLUX.1-dev set true_cfg_scale above 1 and supply negative_prompt, accepting about double compute (two passes); for schnell leave guidance at 0 and put exclusions into the positive prompt wording. Failure modes. Using a negative prompt with only guidance_scale set may do nothing (inference; the docs do not say so explicitly). Limitations. I did not read the pipeline source to confirm that negative_prompt is ignored when true_cfg_scale <= 1. Rights. schnell Apache 2.0; dev, Krea dev, Fill dev and Kontext dev use the FLUX.1-dev Non-Commercial License per BFL docs. Version/date. diffusers main, fetched 2026-10-23. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Whether negative_prompt is silently ignored without true_cfg_scale is inferred; verify in code. Hosted FLUX endpoints may differ. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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    {
      "url": "https://raw.githubusercontent.com/huggingface/diffusers/main/docs/source/en/api/pipelines/flux.md",
      "note": "Timestep-distilled; Guidance-distilled; IP-Adapter example; Fill Inpainting/Outpainting; Canny Control; Open-weight models; Open-weight models; reading"
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    {
      "url": "https://raw.githubusercontent.com/black-forest-labs/flux/main/docs/text-to-image.md",
      "note": "Timestep-distilled; Guidance-distilled; IP-Adapter example; Fill Inpainting/Outpainting; Canny Control; Open-weight models; Open-weight models; reading"
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