Qwen3.8-27B UD-Q3_K_XL โ€” MLX imatrix-direct (native MLX, dynamic quant)

Native-MLX port of unsloth's UD-Q3_K_XL dynamic quantization for Qwen/Qwen3.8-27B. Runs the quantizer search natively in MLX's affine format (group size 64) and writes final MLX weights directly โ€” no GGUF round-trip, no mlx_lm.convert re-quantization.

Perplexity (wikitext-2-raw first 32k tokens, 512-token windows):

Build PPL โ†“
unsloth UD-Q3_K_XL GGUF in llama.cpp 8.136
this model 8.136

The GPTQ variant of this build (jclyons52/Qwen3.8-27B-UD-Q3_K_XL-MLX-gptq-direct) improves this to 8.090 and is the recommended Q3 download.

Method

  1. Bit map from unsloth's Qwen3.8-27B-UD-Q3_K_XL.gguf (dynamic per-tensor bit allocation).
  2. Importance-weighted affine search per group using unsloth's published imatrix (per-column activation energies).
  3. Final MLX weights emitted directly (packed uint32 codes + bf16 scales/biases) โ€” the emitted weights are exactly what the search chose.

Limitations

  • Affine vs IQ-codebook gap. MLX quantized matmul supports only uniform affine grids; unsloth's โ‰ค3-bit GGUFs use non-linear IQ codebooks. The gap vs GGUF is inherent to MLX's current kernels, not the weights.
  • Text-only. The base checkpoint's visual tower is not included.
  • Eval scope: wikitext-2, 32k tokens only; downstream tasks uncharacterized.
  • Not for further training.

Calibration data

Importance weighting: unsloth's published imatrix_unsloth.gguf.

Credits

Built 2026-08-28. Base model license inherited from Qwen/Qwen3.8-27B.

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