Huihui-Qwen3.8-27B-abliterated-NVFP4

NVFP4 (4-bit) quantization of huihui-ai/Huihui-Qwen3.8-27B-abliterated, produced with NVIDIA TensorRT Model Optimizer 0.45.0 with a six-source diversity calibration set (chat / multilingual / reasoning / agentic tool-call traces / few-shot completion formats). Ships the fixed chat template from froggeric/Qwen-Fixed-Chat-Templates (v22.4).

Read this first: template default and token budget dominate benchmark scores

Every GSM8K number below is the same base model measured under different protocols:

• Real capability is intact — ~0.98 for both builds; the quantization delta is within noise.
• The official template's xhigh default causes overthinking that exhausts any reasonable budget (0.59 for the unquantized base). The shipped template defaults to medium.
• The 4-bit checkpoint drifts away from raw few-shot completion format (spontaneously opens <think>, then cannot fit its answer in 256 tokens). This held for four different calibration sets (raw GSM8K 0.598–0.601 in all four) — it is a property of the quantized weights, not of calibration. No impact on chat/agent usage; do not feed this model raw few-shot prompts.

Quantization

• Format: NVFP4 weights (group size 16) + FP8 KV cache, ModelOpt 0.45.0 (hf_ptq.py), calib_seq=2048
• Calibration (5349 samples, six sources) — build scripts in scripts/:

• Excluded modules: lm_head, embeddings, linear-attention conv1d/in_proj_a/in_proj_b, MTP layers, vision tower.
• Empty-think fix (important): both trace datasets ship with thinking stripped (empty <think> blocks). An intermediate build calibrated on those raw traces regressed badly in chat mode (GSM8K 0.6283; ~26% of generations emitted a one-line thinking preamble and then stopped). Fix: every assistant turn gets short synthetic reasoning_content and windows end only on natural boundaries (scripts/build_v4_traces.py). With the fix, chat GSM8K returned to 0.9833.

Validation: xhigh thinking-runaway gate (9 cases)

gate9_cases.json (included): FR/EN long-form × temp {0, 0.7} × reasoning_effort=xhigh, 32k budget, 8-gram decile copy-rate analysis (separates genuine extended thinking from repetition loops).

Differences vs the BF16 base are within run-to-run variance; every terminal runaway across every build occurred at or near temperature 0. At the default medium effort no runaway was ever observed in any protocol.

Known runtime issue (affects all builds of this model family on sglang)

Under 64 concurrent requests × 8192-token generations, sglang 0.5.17 crashes (0-element reshape in the linear-attention path, likely a mamba-pool retraction edge case). This is weight-independent (v2 and v4 both crash). Mitigations: lower --max-running-requests, cap per-request max_tokens, or upgrade sglang.

Usage

CUDA_VISIBLE_DEVICES=0 python -m sglang.launch_server \
  --model-path <this-checkpoint> \
  --quantization modelopt \
  --trust-remote-code \
  --mem-fraction-static 0.8

import requests
requests.post("http://127.0.0.1:30000/v1/chat/completions", json={
    "model": "Huihui-Qwen3.8-27B-abliterated-NVFP4",
    "messages": [{"role": "user", "content": "..."}],
    "temperature": 0.7,
    "max_tokens": 8192,
    # only for maximal deliberation (see gate notes):
    # "chat_template_kwargs": {"reasoning_effort": "xhigh"},
})

Tool calls: the template renders OpenAI-style tool_calls/tool history as Qwen <tool_call> XML and tolerates stringified-JSON arguments. History assistant turns render empty <think> blocks by default (canonical Qwen behavior); pass preserve_thinking=false to omit them entirely.

Plain transformers/BF16 inference will not dequantize this checkpoint; use sglang --quantization modelopt or TensorRT-LLM. 5 shards, each ≤ 5 GB (~19.5 GB total).

Deployment recommendations

1. Leave reasoning_effort at the default (medium) — worth +39 GSM8K points over xhigh under a 2048-token budget.
2. max_tokens headroom 8k+; the answer follows the closing </think> tag.
3. If xhigh is required: temperature > 0, repetition_penalty ≈ 1.05, cap + retry at medium.
4. Cap concurrency for long generations (see runtime issue above).
5. Do not use raw few-shot completion prompts.

License

Apache 2.0 (inherited from the base). Credit to huihui-ai for the abliterated base, froggeric for the fixed chat template, and the authors of the two trajectory datasets used for calibration.