Ornith-1.5-35B-A3B-abliterated-NVFP4

NVFP4 (W4A16) quantization of an abliterated (refusal-direction removed) build of ornith-ai/Ornith-1.5-35B-A3B.

The per-layer quantization recipe is matched exactly to the official ornith-ai/Ornith-1.5-35B-A3B-NVFP4; the only difference is the underlying weights, which come from the abliterated model.

20 GB, runs on 2×16 GB consumer GPUs (tested on 2× RTX 5070 Ti, TP2).

⚠️ Text-only. The abliteration was performed on a language-model-only export, so this checkpoint contains no vision tower and no MTP head (the official NVFP4 release keeps both). --language-model-only is therefore unnecessary — there is nothing to skip.

⚠️ Uncensored. Safety refusal behaviour has been deliberately removed. You are responsible for how you use it.

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1. How the abliteration was done

Classic refusal-direction ablation (orthogonalization), single direction:

This projects the refusal direction out of the output space of the attention- and MLP-output projections. Tooling derived from remove-refusals-with-transformers.

The BF16 abliterated weights are published separately at pottokao/Ornith-1.5-35B-A3B-abliterated.

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2. How the quantization was done

NVIDIA TensorRT Model Optimizer 0.45.0 (same version as the official release), RTN for weights, max calibration for activations.

Calibration: 64 samples × 512 tokens from abisee/cnn_dailymail (3.0.0). Only the 130 FP8 (W8A8) projections need calibration; all NVFP4 parts are weight-only.

Verification against the official release

Tensor-level audit vs ornith-ai/Ornith-1.5-35B-A3B-NVFP4:

weight_scale_2   30841  ==  official 30841   OK   (40×256×3 + 120 + 1)
input_scale        130  ==  official   130   OK   (30×3 + 10×4)
quantized_layers   291  ==  official   291   OK   (FP8 130 + W4A16_NVFP4 161)
quant_algo   MIXED_PRECISION == official      OK
per-pattern diff in the language model: 0

(The only differing patterns are visual.* and mtp.*, which this text-only build does not contain.)

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3. Serving with vLLM + DFlash speculative decoding

The draft model used for all benchmarks below is z-lab/Qwen3.6-35B-A3B-DFlash (0.72 GB, 6 layers, hidden 2048). A copy is included under dflash_draft/ for convenience — original weights and license belong to z-lab.

docker run -d --name ornith --gpus all --ipc=host --network host \
  -v /path/to/Ornith-1.5-35B-A3B-abliterated-NVFP4:/model \
  vllm/vllm-openai:nightly \
  /model --host 0.0.0.0 --port 8009 --tensor-parallel-size 2 --trust-remote-code \
  --kv-cache-dtype fp8 --attention-backend TRITON_ATTN --moe-backend humming \
  --gpu-memory-utilization 0.93 --max-model-len 131072 \
  --max-num-seqs 4 --max-num-batched-tokens 2048 --enable-chunked-prefill \
  --speculative-config '{"method":"dflash","model":"z-lab/Qwen3.6-35B-A3B-DFlash","num_speculative_tokens":8,"moe_backend":"humming","attention_backend":"TRITON_ATTN"}' \
  --reasoning-parser qwen3 --tool-call-parser qwen3_xml --enable-auto-tool-choice

Memory / KV budget on 2× 16 GB

The KV pool is shared, so --max-model-len 131072 and --max-num-seqs 4 coexist fine — but 4 concurrent requests cannot each hold a full 128 K context (vLLM reports Maximum concurrency for 131,072 tokens per request: 2.26x). The pool is this large because only 10 of 40 layers use full attention; the other 30 are linear-attention (Mamba-style) layers that keep a fixed-size state instead of a growing KV cache.

Do not push --gpu-memory-utilization to 0.95. Startup fails with a CUDA OOM inside the sampler warm-up: the top-k/top-p Triton buffer needs batch × vocab(248320) × 4B ≈ 62 MiB, which vLLM's memory profiler does not reserve. 0.93 leaves enough headroom.

Kernels actually selected: attention TRITON_ATTN, MoE humming, linear layers Marlin (the only NVFP4 W4A16 path on sm120), sampling FlashInfer.

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4. Benchmarks

Hardware: 2× RTX 5070 Ti (16 GB, 250 W), TP2, PCIe Gen5. Config: 128 K context, max-num-seqs 4, DFlash K=8, FP8 KV, util 0.93.

4.1 Spec-Bench style suite (vllm bench serve, 8 prompts/category, concurrency 1, 8 warm-ups)

4.2 Single-stream by prompt type (end-to-end, temperature 0.6)

Acceptance depends heavily on the prompt type — anywhere from 1.65 to 5.73 accept_len on the same model and config. Structured output (math, code, JSON) drafts very well; free-form Chinese prose drafts poorly. Always report the prompt mix alongside an acceptance number.

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5. AIME 2026 — sanity check only

This is not a capability benchmark. It exists solely to check that abliteration + NVFP4 quantization did not cause catastrophic degradation (looping, gibberish, broken arithmetic). There is no external baseline to compare against — neither the base model card nor the official NVFP4 release reports AIME 2026 — so these numbers can only rule out loud failure modes. They say nothing about how this model ranks against the original, unquantized LLM.

Setup: serial, concurrency 1 (hard-reasoning benchmarks must not be run concurrently), thinking enabled, max_tokens=96000, top_p=0.95, top_k=20, answer parsed from \boxed{N}. A question was retried when it was wrong or hit the token limit.

39 attempts across 30 questions, ~1.41 M generated tokens.

The three that did not pass first time

Every failure was non-termination — the model burned the full 96 K budget without converging. Not a single question was failed by producing a wrong answer. That distinction matters for a sanity check: the failure mode is "kept thinking", not "computed garbage", which is what a badly damaged quantization would look like.

Q15 converged exactly once (high temperature, 1194 tokens) and answered 3766 — outside AIME's valid 0–999 range — after misidentifying the problem as USAMO 2017 P6. That is a "doesn't know how to solve it" failure, not a degradation artifact.

Retrying non-termination: temperature, not tokens

Q30 was retried three times at the same temperature and truncated all three times, then solved on the second attempt at temperature 0.9. Q29 followed the same pattern. Raising max_tokens does not help this failure mode either. If you hit finish_reason: length on a reasoning task, change the sampling temperature rather than re-running identical parameters or adding tokens.

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6. Provenance

ornith-ai/Ornith-1.5-35B-A3B  (BF16, MIT)
        └── refusal-direction ablation (layer 24, o_proj + down_proj)
                └── pottokao/Ornith-1.5-35B-A3B-abliterated        (BF16, 65 GB)
                        └── modelopt 0.45.0 NVFP4, recipe matched to official
                                └── this repo                      (20 GB)