redashes/Qwen3.8-27B-BF16-SSMFIX-apostate

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Qwen3.8-27B-BF16-SSMFIX-Apostate

A selective-unlearning variant of Qwen3.8-27B built on the SSMFIX BF16 base, produced with the apostate KCRN method (Kernel Constraint Rank-Nullity projection). The model removes most refusal behaviors while keeping language-model capabilities close to the original.

Model Overview

Derivation

This model is derived from [redashes/Qwen3.8-27B-BF16-SSMFIX](https://huggingface.co/redashes/Qwen3.8-27B-BF16-SSMFIX) — a conv1d-repaired BF16 variant of Qwen3.8-27B (SSMFIX-v2, with per-layer α-scaling on 8 anomalous SSM layers). The KCRN edits (42 weight patches) are applied on top of this base without modifying the conv1d repair weights.

Base model repository: https://huggingface.co/redashes/Qwen3.8-27B-BF16-SSMFIX

Method

apostate KCRN (Kernel Constraint Rank-Nullity) — a closed-form, analytic unlearning algorithm by heterodoxin:

1. 1.Compute a low-rank "refusal subspace" Q_b from the refusal direction residuals in MLP blocks (mlp.down_proj ×35, linear_attn.out_proj ×5, self_attn.o_proj ×2, 42 edits total).
2. 2.Project the edit onto the null-space of Q_b (ΔW ⊥ Q_b), which structurally guarantees the refusal information is removed while normal generation directions are preserved.
3. 3.No iterative tuning, no adversarial prompts — the projection is computed in a single solve.

This makes the KL divergence between base and edited model analytically bounded rather than empirically tuned.

Original project: github.com/heterodoxin/apostate — the KCRN unlearning library this model is built with.

Capability Benchmarks

Unified evaluation methodology (vLLM local-completions API, max_gen_toks=2048), same caliber as the baselines:

Key takeaways:

• —Knowledge retention: CMMLU −0.67pp vs official, +1.62pp vs SSMFIX base.
• —Math reasoning: GSM8K nearly identical to base (−0.15~−0.31pp).
• —Truthfulness (mc): small dip (−1.6~−1.9pp vs official).
• —Truthfulness (gen): better than official BF16 (bleu/rouge +1.2~+2.1).

Refusal Behavior

The unlearning targets harmful categories broadly. Overall refusal rate: 7/100 (7%) — measured on harmful_1000[800:900] (100 prompts, content-only judgment after removing keyword false positives); delivery rate ≈ 93%.

Remaining refusal is concentrated in a few legally-sensitive directions:

KL Divergence

Two numbers exist for this model — the original report value and the verified true value:

Usage

from transformers import AutoModelForCausalLM, AutoTokenizer

model = AutoModelForCausalLM.from_pretrained(
    "redashes/Qwen3.8-27B-BF16-SSMFIX-apostate",
    torch_dtype="bfloat16",
    device_map="auto",
)
tokenizer = AutoTokenizer.from_pretrained("redashes/Qwen3.8-27B-BF16-SSMFIX-apostate")

messages = [{"role": "user", "content": "你好"}]
text = tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
inputs = tokenizer([text], return_tensors="pt").to(model.device)
out = model.generate(**inputs, max_new_tokens=512)
print(tokenizer.decode(out[0], skip_special_tokens=True))

vLLM serving:

vllm serve /path/to/Qwen3.8-27B-BF16-SSMFIX-apostate \
  --served-model-name Qwen3.8-27B-BF16-SSMFIX-apostate \
  --tensor-parallel-size 1 \
  --max-model-len 8192 \
  --kv-cache-dtype fp8_e4m3 \
  --enable-chunked-prefill

Note: the chat template enables thinking by default (Qwen3.5 template). Set enable_thinking=False if you want direct responses.

Disclaimer

This is an experimental research model derived from Qwen3.8-27B via unlearning. It is provided as-is without guarantees. Users are solely responsible for compliance with applicable laws and the original base model's license terms. Do not use for disallowed purposes.