Qwen3.5-4B (Yooz QAT, GGUF Q4_0)

What this is

The GGUF (Q4_0) release of Yooz Labs' quantization-aware-trained (QAT) Qwen3.5-4B -- the same weights as Qwen3.5-4B-qat-lean-4bit-mlx, converted for llama.cpp. Stock 4-bit PTQ builds of this model break its aggregation abilities outright (variable-tracking collapses to 0.00 on the MLX product grid); this build is trained to tolerate 4-bit quantization via knowledge distillation from the full-precision bf16 model, so the quantized weights reproduce the original model's behavior -- aggregation AND multi-turn recall -- at both short and long context.

Provenance

  • Base checkpoint: Qwen/Qwen3.5-4B
  • QAT training: Yooz Labs, 2026-07 -- knowledge distillation from the bf16 base model under fake-quantization matching the MLX 4-bit group-64 grid (the training target; this GGUF is the same trained weights re-quantized to Q4_0 for llama.cpp). Full-parameter training at this size. Training recipes are not published.
  • Conversion: llama.cpp convert_hf_to_gguf.py + llama-quantize to Q4_0 (build e3546c7). The converter's block count is set to 32 layers, matching this model's actual depth.
  • Harness: benchmarks/ (infinite repo, Yooz Labs).

Validation

The comprehensive A/B (needle-in-a-haystack, RULER-style aggregation, MRCR) was run on the MLX build of these exact weights, since that is where the full n=30, two-context-length harness lives; see Qwen3.5-4B-qat-lean-4bit-mlx for the full table and chart. Summary:

Task Context 4-bit PTQ, same grid Yooz QAT 4-bit
NIAH single 8K 1.00 1.00
NIAH multikey 8K 1.00 0.97
Variable tracking 8K 0.00 0.97
Frequent words 8K 0.12 0.83
MRCR 2-needle 8K 0.97 0.97
NIAH single 32K 0.97 1.00
NIAH multikey 32K 1.00 0.97
Variable tracking 32K 0.89 0.99
Frequent words 32K 0.22 0.77
MRCR 2-needle 32K 0.96 0.96

This GGUF file was separately spot-checked through the actual llama.cpp Q4_0 path (not just the MLX grid) at 8K context, n=30, on an A100-SXM4-80GB (AMD EPYC 7713, Ubuntu 22.04, llama.cpp build e3546c7):

Task Context Yooz QAT 4-bit (this GGUF file)
Variable tracking 8K 0.96
Frequent words 8K 0.62
MRCR 2-needle 8K 0.94

Consistent with the MLX numbers above -- the fix survives re-quantization to a different format.

Usage

llama-cli -m Qwen3.5-4B-qat-Q4_0.gguf -p "List the first five prime numbers." -n 64

Or with llama-server for an OpenAI-compatible endpoint:

llama-server -m Qwen3.5-4B-qat-Q4_0.gguf --port 8080

An MLX build of the same QAT weights is available at YoozLabs/Qwen3.5-4B-qat-lean-4bit-mlx.

About Yooz Labs

Maintained by Yooz Labs -- sovereign, on-device AI for macOS. Everything we ship runs locally; nothing goes to a cloud. This build comes out of our long-context research line, where we found and quantified the PTQ aggregation crater -- and then trained it away.

Questions, issues, or corrections: dev@yooz.info

License and attribution

Apache 2.0, inherited from the base checkpoint Qwen/Qwen3.5-4B. Qwen is a model family by Alibaba Cloud; this is an independent, unofficial QAT build, not distributed, endorsed, or certified by Alibaba.

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