Qwen3.5-9B · NVFP4 (W4A4, FP4)

4-bit quantization of Qwen/Qwen3.5-9B, produced for efficient vLLM serving. Quantized by axteam.

Base model Qwen/Qwen3.5-9B
Method NVFP4 (W4A4, FP4)
Format compressed-tensors nvfp4-pack-quantized
Weights / activations W4A4 — FP4 (E2M1) weights group 16 (FP8 E4M3 scale + per-tensor FP32 global scale), FP4 activations
Architecture Hybrid (linear-attention + full-attention) · Dense · multimodal (vision) · MTP head
Size on disk ~10.9 GB
Calibration 256 samples (Korean-heavy mixed corpus)
License Apache-2.0

Quantization details

  • Scheme — W4A4 — FP4 (E2M1) weights group 16 (FP8 E4M3 scale + per-tensor FP32 global scale), FP4 activations, stored as compressed-tensors nvfp4-pack-quantized.
  • Kept in BF16 — the vision tower & projector (model.visual.*), the multi-token-prediction head (mtp.*), all RMSNorms, token embeddings, the LM head, the entire linear-attention (GatedDeltaNet/SSM) path — FP4 is too coarse for the SSM weights, so the full linear_attn.* stays BF16. Left unquantized to preserve quality (a small fraction of parameters).
  • Tokenizer / chat_template / generation_config are identical to the original. config.json is the original plus a quantization_config block.

This is post-training quantization (PTQ) — no retraining, so behaviour stays faithful to the original. AWQ uses a small calibration set (no gradient) to protect salient weight channels before rounding.

Evaluation (measured)

Fidelity to the BF16 original on an internal mixed English/Korean set (100 prompts, BF16 greedy answers scored under each build — same harness for every row).

Metric This model BF16 original
Perplexity (lower = closer) 1.5459 1.4506 (+6.6%)
Top-1 next-token agreement 90.3% 99.2%

These measure fidelity to the base model, not absolute task scores.

Usage (vLLM)

vllm serve axteam/Qwen3.5-9B-NVFP4

Recommended sampling (Qwen): temperature=0.7, top_p=0.8, top_k=20. This is a Blackwell-only format — it needs FP4 tensor cores (B200) for full speed.

License

Quantized derivative of Qwen/Qwen3.5-9B (Apache-2.0). All original weights, tokenizer and chat template belong to the Qwen team.


한국어 요약

Qwen/Qwen3.5-9B 를 NVFP4 (W4A4, FP4) 로 양자화한 서빙용(4-bit) 모델입니다. 작성: axteam.

  • 방식 — 가중치·활성화 모두 FP4(W4A4). Blackwell(B200) FP4 텐서코어에서 제 속도. 품질 우선이면 NVFP4A16 권장. 형식 compressed-tensors nvfp4-pack-quantized.
  • BF16 유지 — 비전 타워·MTP 헤드·모든 norm·임베딩/LM 헤드·SSM(linear_attn) 경로 전체(FP4가 SSM 가중치엔 너무 거칠어서).
  • PTQ — 재학습 없음, 원본 동작 유지.
  • 품질(실측) — BF16 원본 대비 perplexity 1.5459(원본 1.4506, +6.6%), top-1 일치도 90.3%(원본 99.2%). 내부 영/한 100문항, 같은 하네스.
  • 사용 — vllm serve axteam/Qwen3.5-9B-NVFP4, 권장 샘플링 temperature=0.7, top_p=0.8, top_k=20.
  • 라이선스 — 원본 Apache-2.0 파생물. 가중치·토크나이저·chat_template 권리는 Qwen 팀.
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