mlx-community/LFM3-VL-2B-OptiQ-4bit

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An OptiQ mixed-precision quant of LiquidAI/LFM3-VL-2B, Liquid's LFM3 vision-language model. It reads images and text and answers in text. It is 1.7 GB on disk, down from 3.9 GB at bf16, with a 128k context.

The language model is the LFM3 backbone: short convolutions and attention, with sliding-window attention, so only 6 of its 24 layers keep a full-length KV cache. OptiQ measures each layer's sensitivity and assigns its bit-width from that. The vision tower stays at bf16 in a sidecar, optiq_vision.safetensors.

What it is

Property Value
Base LiquidAI/LFM3-VL-2B
Architecture lfm3_vl: LFM3 language model (24 layers: 13 convolution, 5 sliding-window attention of 256 tokens, 6 full attention) plus a vision tower
Method OptiQ mixed-precision, sensitivity-driven (bf16 reference); vision tower at bf16
On disk 1.7 GB (bf16: 3.9 GB)
Context 128k

About half of the language model's weight matrices stay at 8-bit (75 of 153), the ones whose quantization moved the output most. The rest are at 4-bit.

Capability Score

Six-metric mean, the standard OptiQ eval, run in reasoning mode because the model thinks before it answers by default. The baseline is a uniform 4-bit quant of the same model, scored the same way.

Metric OptiQ Uniform 4-bit
MMLU (generative) 68.9% 70.6%
GSM8K 83.2% 76.4%
IFEval (strict) 44.4% 35.7%
BFCL-V3 simple (200 calls) 91.0% 90.5%
HumanEval (164 problems, pass@1) 55.5% 43.9%
HashHop (long-context retrieval) 3.0% 0.0%
Capability Score (mean of 6) 57.67 52.85

The OptiQ quant is ahead by 4.8 points overall, with the largest gains on code (+11.6), instruction following (+8.7) and math (+6.8).

Run it

pip install -U mlx-optiq
optiq serve --model mlx-community/LFM3-VL-2B-OptiQ-4bit

That gives you an OpenAI and Anthropic compatible endpoint that takes images as well as text, with mixed-precision KV cache (kv_config.json in this repo), tool calling, and prompt caching. Send an image as an image_url content part, as with any OpenAI vision request.

The model reasons before it answers, so give it a generous max_tokens. Liquid's recommended sampling (temperature 0.1, top_k 50, repetition_penalty 1.1) ships in generation_config.json, and optiq serve applies it automatically.

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