MiniMax-H3-MLX-f32

MLX (Apple Silicon) build of the MiniMax-H3 diffusion transformer. Unquantized, upcast to float32.

Powered by MiniMax H3.

These files are modified. The transformer weights have been converted to MLX and widened to float32; they are not MiniMax's originals. Everything else about the model is unchanged.

What this is

MiniMax-H3 generates synchronized video and audio together. It is not a language model: a 33B diffusion transformer denoises video and audio latents jointly over one packed sequence, conditioned by a frozen Qwen3-VL-32B encoder, with separate video and audio VAEs. Running it needs the pipeline code, not just these weights:

git clone https://github.com/PipeNetwork/minimax-h3-mlx
cd minimax-h3-mlx && pip install -r requirements.txt
python scripts/generate.py "a red fox leaps over a mossy log" -o fox.mp4

This repository holds the transformer only. The VAEs and the text encoder come from the upstream release; the pipeline loads them directly.

Size

The gap is deliberate. ~13B of H3's 33B parameters are the per-block AdaLN projections, whose only input is the timestep embedding. For a fixed sampler schedule every modulation tensor a run needs is precomputed once into a small table, and the projections are then dropped — so they are on disk but never resident. The table scales with step count, not model size: measured at 145 MB for a 9-step schedule and 745 MB for 40 steps, against the 26 GB it replaces.

This build carries no more information than the bf16 one. MiniMax's weights are bfloat16 on disk, so upcasting to float32 is a lossless widening, not extra precision — you are downloading 132.6 GB of data that fits losslessly in 66.3 GB. It is published for float32 fine-tuning and numerics work, where having the base already widened is convenient.

If you only want to generate, take bf16 instead. If you want float32 compute from a smaller download, load_dit(dtype=mx.float32) upcasts at load time and gives an identical model.

How the widths compare

Measured with teacher forcing — one bfloat16 trajectory recorded, each variant re-predicting the velocity at those same latents, so the difference is quantization error alone rather than trajectory divergence. 20 paired observations per variant, aggregated with a paired bootstrap.

Every interval is disjoint from its neighbours, so the ranking is solid. Two things worth noting: the steepest step is 6 to 4 bits (2.7x), not at the low end; and audio degrades faster in relative terms than video (its share of the error climbs from 0.40x at 8-bit to 0.82x at 3-bit), plausibly because audio is a small fraction of the packed rows and has less redundancy to absorb it.

Why 8, 6 and 4 bits only

Velocity error ranks the widths but does not say where output stops being usable — the scheduler integrates velocity, so per-step error compounds along the trajectory. That has to be generated to be seen. The same prompt, seed and settings were rendered through each checkpoint and compared to bfloat16:

At 3 bits the scene is gone — no animal, no log, just a textured field. It is built but not published. Notably it does not degrade by blurring: its per-frame variance rises (54.7 against bfloat16's 37.1) as structure is replaced by high-frequency noise, so a sharpness metric would have scored it as healthy. 2-bit is not published either; extrapolation puts it near 50% velocity error.

6-bit was not rendered separately — it is bracketed by 8-bit and 4-bit, which both pass.

Read this before choosing a quant

MiniMax has not released its sparse-attention implementation, so inference runs dense attention over tens of thousands of rows. On an M3 Ultra a single denoising step costs about 8.8 minutes for a 5-second clip (37,966 packed rows) and 1.04 hours for 15 seconds (109,318 rows).

Quantization does not change that. The bottleneck is attention FLOPs, which quantization does not reduce; the linear layers are ~42% of the work at 5 s and ~20% at 15 s, so a 4-bit build is worth roughly 1.2-1.4x end to end. Choose a quant to fit H3 on your machine, not to make it quick.

Licence

Governed by the MiniMax H3 Community License, a copy of which is included in this repository. It is not an open-source licence. Notably: redistribution must carry the agreement and mark modified files; commercial products above $20M yearly revenue need separate authorization from MiniMax; and the grant is territorially limited (worldwide, excluding the Excluded Territories defined in the agreement). By downloading these weights you accept those terms.

The MLX port code is Apache-2.0 and lives at https://github.com/PipeNetwork/minimax-h3-mlx.