MATLOWAI/minimax-h3-nvfp4

MiniMax H3 FL2VA pruned, NVFP4 (Blackwell)

An NVFP4 quantisation of the MiniMax H3 pruned FL2VA diffusion model for ComfyUI. Every one of the 200 block linears (qkv, out, fc1, fc2 in all 50 blocks) is stored as fp4 e2m1 with fp8 e4m3 block scales of 16 and one fp32 per-tensor scale; embeds, token refiner, norms and heads stay bf16. On Blackwell (sm120) the GEMMs run natively on the fp4 tensor cores.

Modification notice (required by the license): this repository contains a modified version of MiniMax H3. The modification is post-training weight quantisation of the block linears to NVFP4, performed 2026-08-19. Built from diffusion_models/minimax_h3_fl2va_pruned_bf16.safetensors in Comfy-Org/MiniMax-H3, revision 3f57e8291d2ef846f9a074b1b76d2767db434abe.

Should you use this file?

• RTX 50-series / Blackwell + pytorch cu130+, current ComfyUI: yes, if you want the speed. Measured against the W4A8 file on the same seed and graph: 0.84x wall at 29k tokens, 0.90x at 45k, on an RTX PRO 6000. Same file size as W4A8 (12.5 GB, both 4.54 bits per parameter), so this is a speed play, not a memory play.
• Any other GPU: no. ComfyUI falls back to dequantised matmuls, which is slower than int8_convrot. Use Comfy-Org's int8_convrot file instead.

Runs on stock ComfyUI, no custom nodes required: the file carries per-layer comfy_quant metadata, the same mechanism as the NVFP4 text encoder that Comfy-Org already ships.

How to run it

1. Blackwell GPU (RTX 50 series or RTX PRO Blackwell), pytorch built for CUDA 13.0 or newer, and a current ComfyUI updated together with its comfy-kitchen dependency.
2. Put the .safetensors in models/diffusion_models/minimax_h3/ next to the usual H3 stack from Comfy-Org (text encoder, video VAE, audio VAE).
3. Use any H3 workflow and point UNETLoader at this file, weight_dtype default. No custom nodes; the per-layer metadata does the rest.
4. Check the load log for Native ops: nvfp4. If a render comes out slower than the int8 file you are on the dequant fallback (wrong pytorch or a stale comfy-kitchen).
5. The lightx2v turbo LoRA stacks cleanly and keeps the speed: measured 12-step turbo, 210 s vs 239 s on the W4A8 file (0.88x), same graph and seed.

What it costs in quality

Median weight error is 9.4 percent relative rms vs bf16 (the W4A8 file carries 7.3, int8_convrot 1.0). In practice a same-seed render is a clean sibling take: same scene and words, slightly different delivery. Side-by-side pages with clips, pixel, flow and audio rulers, and a synced A/B player: https://matlowai.github.io/ComfyUI-MAINodes/a6-review/ (the gold cards are this checkpoint). Note that an int8 control lands in the same distance-from-reference band, so within this model family that distance measures which take you got, not how good it is. Judge with your eyes on your own content.

The other regimes, and why only this one is published

Three other real NVFP4 regimes were built and rendered on the same scene, seed and graph (a fourth, except_out, was built but never rendered). All three are dominated by this file on every axis that can be trusted, so none of them is published as a checkpoint:

regime	what stays fp4	size	wall	VRAM
all (this file)	qkv, out, fc1, fc2 in all 50 blocks	12.5 GB	421.2 s	59.3 GB
mid	the same four, blocks 2 to 47 only	14.7 GB	432.2 s	65.2 GB
nofc2	qkv, out, fc1 (fc2 stays bf16)	18.0 GB	450.8 s	63.9 GB
fc1	fc1 only	29.1 GB	525.6 s	75.8 GB
int8 convrot (the A8W8 file)	nothing, int8 everywhere	21.0 GB	458.5 s	82.5 GB

Leaving layers in higher precision makes the file bigger, the render slower and the peak VRAM higher, which is what you would expect. What it does not do is give you a defensible quality win, because within this family we cannot measure one. Every arm is a sibling take of the reference: same scene and words, slightly different delivery. The control that settles it is the int8 checkpoint in the last row, which carries about 1 percent weight error and should be the quality ceiling of the whole quantised family. It has the best pixel PSNR (14.76) and the best flow agreement (0.549) of any arm, and simultaneously the worst audio correlation (0.147 against 0.329 to 0.528 for the fp4 arms) and the worst mel error. A distance metric that ranks the most faithful checkpoint last on audio is not measuring quality. Judge with your eyes and ears on your own content.

Measurements and per-layer censuses

Published here because they are hard to obtain and easy to carry, not because they rank anything:

• census/ plus the .census.json beside the weights: the per-layer NVFP4 weight error (rel_rms_nvfp4, one row per quantised linear) for six builds, with the source file, build time and scale mode in each meta block. Includes ..._all_staticscale, a calibrated-static-input_scale build that is a negative result and is not published as weights: static scales did not make streamed inference exact (streamed-vs-unstreamed rel-rms 0.392 static against 0.364 dynamic, so slightly worse), which located the remaining streaming difference outside the linears.
• measurements/: the full metric set behind the review site, 59 arms over three scenes (bakery 6, painters 19, spider 34), each with pixel, flow and audio rulers plus per-frame curves. Most arms are fake-quantised activations on the shipped W4A8 model, one region at a time; the rows tagged real checkpoint are native fp4 kernels. Rendered side by side with a synced head-to-head player at https://matlowai.github.io/ComfyUI-MAINodes/a6-review/

Rebuild it yourself

The 30-second builder script (quantises the Comfy-Org bf16 file with comfy's own TensorCoreNVFP4Layout) ships in ComfyUI-MAINodes as tools/build_nvfp4_checkpoint.py. The .census.json beside the weights holds the per-layer weight error of this exact build.

License

MiniMax H3 Community License Agreement (see LICENSE and NOTICE in this repository, and the license link above). The license carries territory restrictions and other conditions; read it before using or redistributing. Powered by MiniMax H3.