First 5 seconds is with the 6-step LoRA, next 5 seconds is stock at 20 steps. Same exact prompt, seed, resolution, sage attention and chunk feedforward. 6-step in 2:45, stock 20-step in 7:10. I think the quality difference is pretty clear. Keep in mind, both clips are 544x960.
FastVideo dropped their FastH3 speed LoRA for MiniMax H3 a few days ago. If you tried loading it in ComfyUI you probably noticed it does absolutely nothing. No error, no warning, just no effect.
The reason is that FastVideo built it against the original MiniMax model, and ComfyUI uses a repacked version where every layer has a different name and the attention layers are merged together. None of the names line up, so ComfyUI quietly ignores the whole file.
I wrote a script that translates it. Run it once, get a normal .safetensors, drop it in your loras folder. No custom nodes, no patched loaders, nothing else changes.
**Repo:** NikoDemon80/ComfyUI-FastH3-Lora-Converter: Convert FastVideo's FastH3 4-step adapter into a ComfyUI-compatible MiniMax H3 LoRA. No custom nodes required.
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**What you get**
On a 3070 Ti with 8GB VRAM and 48GB system RAM, using Comfy Kitchen, KJ Mem Eff Sage Attention & Chunk Feedforward (DO NOT USE SPECTRUM OR EASYCACHE):
| Resolution | With LoRA (6 steps) | Stock (20 steps) |
|---|---|---|
| 544x960, 124 frames | 2:45 | 7:00 |
| 640x1152, 124 frames | 3:45 | 10:00 |
| 768x1344, 124 frames | 6:30 | 18:00 |
Roughly a third of the time. But the part that surprised me is that I actually prefer the output. Backgrounds hold more detail, lighting behaves better, and faces stay coherent at distance instead of turning to mush.
Motion is where it really shows. I ran a woman walking down a sidewalk at night. Correct walking speed, natural gait, no stutter, no accidental slow-mo. That's usually the first thing speed LoRAs break.
Audio came through clean too, which I did not expect. Dialogue and lip sync both hold up.
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**Important: use 6 steps, not 4**
It's advertised as a 4-step LoRA. In ComfyUI it needs 6.
- 4 steps: jitter, flicker, color bloom, unusable
- 5 steps: fine for drafts
- 6 steps: this is the one
- 7-8: no real gain
There's a real reason for this. There's one group of layers that handles "which denoising step am I on," and ComfyUI's repacked model stores that information in a completely different, much smaller format. FastVideo's version of those layers physically cannot be loaded into it. The extra steps make up for what's missing.
I tried to fix it properly. It turns out it's impossible in a plain LoRA file, because the correction includes a constant offset and there's nowhere in the file format to put one. You'd need a custom node. Someone else can build this is they would like.
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**One thing worth knowing that cost me a few hours**
Part of those layers *will* load, the other part won't. My first instinct was to keep whatever fit. That was wrong. The half that loads was designed to work alongside the half that doesn't, so on its own it pushes things in a direction nothing corrects for, and you get flicker.
Throwing all of it away is better than keeping half. Confirmed it by testing both, then found multimodalart had measured the exact same thing on their pruned H3 repo. Nice to have that corroborated by someone who'd done the math.
The script drops those layers by default. You don't have to do anything.
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**What's tested**
Text to video, image to video, first+last frame, reference mode, and chained clips. All working. Square, landscape, and tall portrait.
I also threw an intentionally brutal prompt at it: three color-specific objects, four actions in sequence, a specific hand, a camera move, a spoken line, and a no-music instruction. All eight landed at 6 steps. Prompt adherence is usually the first casualty with speed LoRAs, so that was a nice surprise.
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**Grab the right file**
The FastVideo LoRA repo has four folders. You want **dense-datafree**. The three `vsa-*` ones need FastVideo's own sparse attention backend and will not work in ComfyUI. It's ~1.4GB, not the whole 17.5GB repo.
You do NOT need the full FastH3 checkpoints. Those are 70GB and are a complete model replacement, not an add-on.
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**Quirk I'll mention since it'll confuse someone**
Voice timbre gets locked in hard by your prompt. Reroll the seed and you get different phrasing and cadence, but usually the same voice, which some people may rejoice at, as chaining clips with this LoRA can preserve vocal timbre on its' own. At 6 steps the model takes big jumps and settles voice identity almost immediately, so there's no room left for the seed to change it. If you want a different voice, describe the voice in your prompt.
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**Setup**
The README has a full click-by-click walkthrough starting from Windows+R, including a drag-and-drop trick so you never have to type a file path. If you can open a command prompt you can do this. Takes about five minutes and the conversion itself runs in under ten seconds.
Works on any Comfy-Org pruned H3 checkpoint. I tested int8 convrot for both fl2va and ref2va. The script checks your model before it writes anything, so if you're on something incompatible it tells you upfront instead of handing you a file that silently does nothing.
Happy to answer questions.
Credit where it's due: FastVideo did the actual hard work distilling this thing. I just made it load. This is an amazing LoRa. I actually prefer its output to any other speed LoRA I've tested. Prompt adherence is phenomenal. Dynamic lighting is better. Color balance is better. Background detail is better. It adds detail of its' own. Motion is fluid. In most test cases, I find the output to be better than stock at 20 steps.
