Qwen3.8-27B — Uncensored on demand

A censored model that uncensors itself when you ask it to — and nothing else changes.

No second 23 GB checkpoint. No baked-in abliterated weights. This is a 2.6 MB pack of direction vectors that plugs into a running vLLM and lets you dial the model's refusal behaviour up or down at runtime, per request, with zero restart:

Two runtimes, one pack of directions. The dial ships for vLLM 0.27.1 and, since 2026-08-29, for SGLang + DSpark — the public DGX Spark recipe. Same vectors, same per-module coefficients, same cache_salt: "refusal:<x>" seal. Measured on the same shared GB10, single stream, T=0: code 26.0 → 56.1 tok/s (2.2×), prose 21.3 → 18.0. Ablation cost on SGLang: zero on code (56.2 vs 56.0), −4% on prose. Port and caveats: runtime/sglang-dspark/.

The same weights, the same pod, even the same batch. One HTTP field switches it.

# server-wide dial
curl -XPOST localhost:8888/admin/refusal_lambda -d '{"lambda": 1}'   # ablation on
curl -XPOST localhost:8888/admin/refusal_lambda -d '{"lambda": 0}'   # off, bit-exact base

Since 2026-08-19 λ can also be set per request, so one pod serves a normal alias and an ablated one from the same weights, in the same batch:

curl -XPOST localhost:8888/v1/chat/completions \
  -d '{"model":"qwen38-27b","messages":[...],"cache_salt":"refusal:1.0"}'

Requests without a salt keep using the global dial. This was documented as dead until now: the obvious implementation is silently wrong, because CUDA graph capture bakes in the global scalar and replay runs no Python — every graph-served decode used the global λ with no warning. The fix binds a per-role buffer to the module at construction, which also keeps it compatible with Dynamo's fullgraph region (measured: compiles once, frames=1, and mutating the buffer does not recompile). Details and the failing-capable tests are in the GitHub README.

Code, patch and benchmarks: https://github.com/pocharlies/qwen38-27b-rank1-refusal-projection

vLLM 0.27.1 runtime update — 2026-08-22

The exact ARM64 compatibility port is published in the GitHub repository under runtime/vllm-0.27.1/. The Unsloth NVFP4 + native MTP k=3 configuration was not changed. It passed health, tooling and refusal-dial checks, but was slightly slower than 0.25.2: 26.01 vs 28.19 tok/s on code and 21.33 vs 21.72 tok/s on the varied workload. Machine-readable results are in benchmarks/2026-08-22/vllm-0.27.1.json.

---

Responsibility & intended use

Read before downloading. This material removes or weakens a model's built-in refusal behaviour on demand. It can make a model answer requests it would otherwise decline — some of them clearly harmful.

• Intended use. Research on interpretability, activation steering and refusal mechanisms (e.g. Arditi et al. 2024), safety evaluation, and legitimate creative/role-play use cases that fall inside your own jurisdiction and terms of service.
• Not intended for. Generating malicious content, fraud, harassment, disinformation, malware, or anything that harms people. No safeguard in this repo will stop those uses; the guardrail is you.
• Legal & policy. The operator of the model is solely responsible for the outputs and for compliance with their local law and the hosting/API terms. This repo is not legal advice.
• The code is the easy part; the deployment is the risk. λ>0 also lowers resistance to prompt injection — do not expose an uncensored alias to content you do not trust (scraped text, inbound mail). Keep /admin/refusal_lambda off any public ingress.
• License. Apache-2.0 code; the vectors derive from publicly released checkpoints and inherit the Qwen license. Use at your own risk.

---

What is in the file

refusal_dirs_qwen38.safetensors — 128 tensors of F32[5120], plus a __coefs__ tensor and a coef_order entry in __metadata__ that pairs them.

Layers 0–63 complete — every sublayer that writes to the residual stream.

The hook is

y ← y − λ · coef_m · r̂ (r̂ · y)

applied to each sublayer output. coef_m is that module's measured λ_eff, so λ=1 reproduces the source ablation profile exactly and λ=0 is the untouched base. The per-module coefficient is not cosmetic: λ_eff ranges 0.999–1.291, and collapsing it to a single mean would introduce up to 21.8 % error on some modules.

How they were derived

SVD of ΔW = W_abl − W_base in float64, per module, between two publicly released checkpoints:

• base: Qwen/Qwen3.8-27B
• abliterated: Zynerji/Ektome-Qwen3.8-27B-PristinelyUncensored

Both BF16, so there is no requantization noise in the difference.

Gates (128 modules)

λ_eff ≈ 1 matters: this source removes the direction exactly once. Baked abliterations often overshoot — the DeepSeek-V4 reference checkpoint sits at λ_eff ≈ 2.43, i.e. it inverts the direction, which measurably costs speculative-decoding acceptance.

Two candidates that did not survive measurement

An s₀/s₁ near 1 means no dominant direction exists. "Abliterated" in a repo name does not make the edit rank-1 — measure before you build on it.

Measured behaviour

Same pod, same prompts, temperature 0, seconds between arms:

The dial costs nothing measurable in throughput on benign work. MTP acceptance is a more nuanced story — see below.

Do not read ~20 tok/s as this model's speed on a DGX Spark. That figure comes from a node whose GB10 is shared by five workloads — this model (33 GB), a vision model (30 GB), two BGE pools and a TTS — hence gpu_memory_utilization: 0.35. The λ=0 vs λ=1 comparison holds, because both arms ran under identical contention seconds apart; only the absolute number is depressed. On a dedicated Spark, an independent user running this exact recipe reported ~40 tok/s (third-party report, not measured here).

Expanded four-lambda benchmark (2026-08-17)

The deployment smoke above has now been followed by a paired evaluation at λ=0, 1, 1.5 and 2.5: 60 StrongREJECT prompts per arm, 100 GSM8K items, 112 balanced MMLU-Pro items, MTP/speed prompt families and an eight-case tool battery.

Against λ=0, the λ=1 quality differences are not statistically detectable in these samples (GSM8K p=0.25, MMLU-Pro p=0.7905). λ=1.5 significantly degrades both suites. At λ=2.5, refusal returns almost to baseline and generation becomes pathologically slow. Abliteration strength is not monotonic after the calibrated edit has been applied once.

Operating point: λ=1. Full methodology, Wilson intervals, paired tests, early-stop records, machine-readable aggregates and the controlled interpretation of Goldhub's Reddit results are in benchmarks/2026-08-17/.

The drafter is not projected, and on refusal topics that costs ~20%

Measured on the served pod, 300 tokens, temperature 0:

Acceptance holds on benign work but drops ~20% on exactly the topics someone turns the dial on for. This was predicted before it was measured: "the patch only touches the main model, not the drafter, so on rejected topics the mini-model keeps refusing and acceptance collapses — the patch has to change the drafter's lambda too."

The effect is real. The proposed cause is not. Projecting the drafter with a backbone direction (VLLM_REFUSAL_MTP_MODE=mean) does not recover it — measured, 3 reps per cell:

0.59 → 0.55 is noise: the benign column alone spans 0.39 across reps.

The control that settles it: at λ=0 the projection is multiplied by zero, so mean and off must be identical. They measured 2.94 and 2.84. That 0.10 is the bench's noise floor, and every "improvement" visible at n=1 sat below it. Do not trust a single sample here.

Best remaining explanation: the backbone already hands the drafter an ablated hidden state, so little refusal signal survives into the drafter's own layer, and the gap is about how hard that content is to predict rather than about who is ablated.

off is the default: it reproduces the source ablation exactly and mean buys nothing measurable.

…and it is not a defect, it is the price of the content

Sweeping λ on the live dial (no restart — that is what the dial is for), 4 triggers each, acceptance measured on a long generation for the same refusal topic:

Acceptance is highest at the λ where the model still refuses, and drops once it starts complying. A refusal is formulaic text the drafter predicts easily; the content produced by complying is novel and it does not. Acceptance tracks what is being generated, not λ — note λ=1.0 scores above λ=0.7, which rules out a monotonic penalty in λ.

So there is no λ that both removes refusal and keeps benign-level acceptance, because the drop is the cost of generating the non-refusal content. Nothing to fix here.

Useful by-product: the dose-response on refusal is clean — 4/4 → 3/4 → 1/4 → 0/4 — and λ=1.0 is the operating point. No reason to go lower, and unlike the DeepSeek-V4 reference (which needed 1.5 and sat at λ_eff 2.43), no reason to go higher.

One direction, not 128

All 128 extracted directions are effectively the same vector — cos against layer 63 is 0.9996 minimum, 1.0000 median, and cos(mean, layer63) = 1.0000. Refusal is mediated by a single global direction in the residual stream, measured here on a 64-layer hybrid with linear and full attention interleaved. It also makes last and mean the same choice.

Limitations

• General capability is sampled, not exhausted. The expanded run covers 100 GSM8K and 112 balanced MMLU-Pro examples; HumanEval and the full benchmark suites were not run.
• Refusal is measured on 60 StrongREJECT prompts per arm, balanced across six categories. Category cells still contain only ten prompts. The 5-trigger/1-control table above is the earlier deployment smoke, not the final rate estimate.
• Long-context retrieval is inconclusive. The planned 32K/128K NIAH run was stopped after 31 minutes of external runtime saturation and received no score.
• Speed/MTP has one replicate, and λ=1.5 retained four of five clean prompts per family after external-load retries were exhausted.
• The MTP drafter is not ablated. Ektome does ship all 15 mtp.* tensors, but they are byte-identical to the base (mtp.layers.0.self_attn.o_proj sha256 9165a16183…), so there is no direction to extract from them. Acceptance stays high anyway. (Corrected: this line previously said the tensors were absent — presence is not ablation.)
• The vision tower is untouched, exactly. 333/333 model.visual.* tensors byte-identical between base and ablation, including merger.linear_fc2.weight, the only one whose output reaches the residual stream. The gap is zero, not merely small.
• λ=0 is bit-exact in output but not free in compute: the dot product and subtraction run in all 128 modules on every token. For zero cost, unset VLLM_REFUSAL_DIRS.

Serving on a DGX Spark: one command

A sparkrun recipe ships next to these vectors — qwen38-27b-nvfp4-refusal-dial.yaml, the exact settings every number above was measured with:

sparkrun run qwen38-27b-nvfp4-refusal-dial.yaml

curl -XPOST localhost:8101/admin/refusal_lambda -d '{"lambda": 1}'   # ablation on
curl -XPOST localhost:8101/admin/refusal_lambda -d '{"lambda": 0}'   # off, bit-exact

It pulls the stock unsloth/Qwen3.8-27B-NVFP4 at model_revision: main — no second checkpoint anywhere. Set container: to your own build of the Dockerfile in the GitHub repo (COPY-only over an existing vLLM image, so it cross-builds to arm64 from x86 without QEMU).

Note on the revision: Unsloth super-squashes their repos, so old pinned SHAs go 404. Don't pin a sha — main is the only revision guaranteed to still exist tomorrow.

Two lines in it are load-bearing: pre_exec runs the fail-closed guard before serving, and --attention-backend triton_attn is not optional on vLLM 0.25.2 — see below.

Exposing it through LiteLLM: two profiles, one pod

The cleanest way to use uncensored on demand in a real deployment is a LiteLLM proxy in front of the vLLM pod. Register the model twice under two aliases that point to the same backend — the only difference is an extra_body.cache_salt that switches λ per request:

model_list:
  - model_name: qwen38-27b              # censored profile (default behaviour)
    litellm_params:
      model: openai/qwen38-27b
      api_base: http://vllm-qwen38.llm.svc.cluster.local:8000/v1   # your vLLM pod
  - model_name: qwen38-27b-uncensored   # uncensored on demand
    litellm_params:
      model: openai/qwen38-27b
      api_base: http://vllm-qwen38.llm.svc.cluster.local:8000/v1   # same pod!
      extra_body: { cache_salt: "refusal:1.0" }

• qwen38-27b (no cache_salt) → vLLM uses the global dial, which boots at λ=0 → the original censored model. Bit-exact.
• qwen38-27b-uncensored (sends cache_salt: refusal:1.0 per request) → vLLM expands that into a per-token λ → the abliterated profile.
• Both aliases hit the same Service, same checkpoint, same GPU, even the same batch. There is no second server. Switching a client from one alias to the other is a one-word change in their model: field.

Cost and security of doing it this way:

• cache_salt enters the prefix-cache block key, so the two aliases keep separate KV cache spaces. That lowers hit rate slightly — and it is the correct behaviour: you do not want a censored request to reuse a block computed under an uncensored λ.
• Gate the uncensored alias by API key in LiteLLM (team/key model access), so only the callers you trust can reach qwen38-27b-uncensored. This is how production isolates it from write-capable tools.

Verified in production on this exact pattern (same Service, extra_body.cache_salt, per-request λ surviving LiteLLM and CUDA-graph replay). The DeepSeek-V4 twin uses the same mechanism at refusal:1.5.

Serving by hand

Requires the vLLM patch in the GitHub repo. Serve the clean checkpoint (or a clean quantization of it — this was validated against unsloth/Qwen3.8-27B-NVFP4) with

VLLM_REFUSAL_DIRS=/path/refusal_dirs_qwen38.safetensors
VLLM_REFUSAL_LAMBDA_INIT=0.0
--attention-backend triton_attn

flashinfer does not serve Qwen3.5-architecture models on vLLM 0.25.2: it starts fine and fails on the first real inference with plan(): Mismatched number of arguments.

Security

Reducing a model's resistance to instructions reduces its resistance to injected instructions arriving inside untrusted content. Prompt injection and refusal route through overlapping machinery.

• λ>0 should not share credentials with write-capable tools.
• Keep /admin/refusal_lambda off any public ingress.

Citation

@misc{arditi2024refusal,
  title  = {Refusal in Language Models Is Mediated by a Single Direction},
  author = {Arditi, Andy and Obeso, Oscar and Syed, Aaquib and Paleka, Daniel and
            Panickssery, Nina and Gurnee, Wes and Nanda, Neel},
  year   = {2024},
  note   = {NeurIPS 2024},
  eprint = {2406.11717},
  archivePrefix = {arXiv}
}

License: Apache-2.0 for the extraction code. The vectors are derived from the difference between two publicly released checkpoints and inherit the Qwen license.