Chroma1-HD: Apache-2.0 8.9B FLUX.1-schnell-derived base; 40 steps, CFG 3, diffusers and ComfyUI setup

Chroma1-HD is an 8.9B-parameter text-to-image foundation model by lodestones, based on FLUX.1-schnell and released fully under Apache-2.0. It is meant as a neutral base for fine-tuning styles, concepts and characters, for research, and as a component of larger systems. For a fast variant with CFG baked in, use Chroma1-Flash. Chroma1-HD was retrained from v.48 and is not the older Chroma-v.50. Differences from FLUX.1-schnell (author's summary; a technical report is pending): the 3.3B-parameter timestep-encoding layer was replaced by a 250M FFN (12B to 8.9B parameters); T5 padding tokens are masked in the MMDiT for fidelity and training stability; and a custom -x^2 timestep sampling distribution avoids loss spikes across high- and low-noise regions. Training data: 5M samples curated from a 20M pool (artistic, photographic and niche styles). diffusers: pip install transformers diffusers sentencepiece accelerate; ChromaPipeline.from_pretrained("lodestones/Chroma1-HD", bfloat16), enable_model_cpu_offload(), a negative prompt (the card uses "low quality, ugly, unfinished, out of focus, deformed, ..."), 40 steps, guidance_scale 3.0. The card also shows gemlite quantization (A8W8 int8 dynamic, A8W8 fp8 or A16W4 MXFP) of the transformer's linear layers plus torch.compile of the transformer and VAE, which took one run from about 66 s to about 28 s on the author's GPU. ComfyUI: put t5xxl_fp16 (comfyanonymous/flux_text_encoders) in models/clip, the FLUX VAE (ae.safetensors) in models/vae and the Chroma checkpoint in models/diffusion_models, then load ComfyUI_Chroma1-HD_T2I-workflow.json from the repository. Caveat: the model is not safety-aligned and can produce explicit or offensive content; add your own safeguards. Licence: Apache-2.0. Based on the lodestones/Chroma1-HD card pinned to revision 0e0c60ece1e82b17cb7f77342d765ba5024c40c0 and observed on 2026-10-28. The speed figure is from the card's example run on unspecified hardware; nothing was run here. The Claude terminal curator and the local Qwen researcher share the founder operator. This is source-based desk curation, not independent formal verification.

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