PXA-Fusion4-35B

PXA-Fusion4-35B — 35B-A3B · abliterated · super-agentic · anti-fabrication

A 35B Mixture-of-Experts model tuned for agentic tool-use, coding, and uncensored reasoning — engineered to run fully GPU-resident on modest and salvaged hardware via PXA's PXQ quantization. Built on a Qwen3.5-35B-A3B foundation, refined through PXA's fusion + calibration pipeline. PXQ2–PXQ6 tiers fit anything from an 11 GB card up. Every quant ships with speculative-decode (MTP) heads and a vision projector.

Probe it. Pick at it. It doesn't fold — and it won't make things up.

Community: Discord — PXA Network · Engine: pxq_llama

Re-download if you pulled before 2026-07-24 - chat template fixed

The first upload shipped a chat template with an inverted enable_thinking default. Unless your client explicitly sent enable_thinking:false, the template pre-filled an unclosed <think> tag, so generation began inside an unbounded reasoning channel. In agentic and coding harnesses this looked like the model planning forever - long first-person prose ("I'll add X. I'll add Y."), no tool calls, no files written, eventually repeating itself until you killed it.

Fixed 2026-07-24. All quant tiers have been re-uploaded. Thinking is now opt-in, matching upstream Qwen: the default renders no-think, and enable_thinking:true still enables reasoning exactly as before.

The weights are unchanged. This was purely the embedded chat template - every tensor is byte-identical to the original upload, only template metadata changed. If you already had it working by passing enable_thinking:false, nothing changes for you.

Running an agent on long open-ended prompts? See Run it below - a thinking budget and Qwen's own presence-penalty recommendation matter a lot there.

What's new vs Fusion2

Fusion4 is the anti-fabrication generation. The headline gain is truthfulness under pressure without losing compliance — a differential graft that imported fabrication-resistance while keeping the model fully uncensored.

How it was built

Fusion4 is not a fine-tune with a new name. It's the output of a multi-stage model-engineering program — weight-space fusion, expert-level surgery, and adversarial-corpus hardening on a Qwen3.5-35B-A3B foundation.

  • Foundation — Qwen 3.5-35B-A3B MoE: 35B parameters, ~3B active per token, 256 experts × 40 layers, hybrid attention (small KV footprint).
  • Fusion + calibration — weight-space blend + imatrix calibration of the expert bank.
  • Anti-fabrication graft — a differential edit that raises false-premise rejection while leaving the uncensored behavior intact.
  • MTP grafting — a speculative-decode head on every shipped quant (inert unless --spec-type is passed).

Quants (pick by your VRAM)

Every quant is MTP-headed (spec-decode ready) and abliterated. Speeds are measured with the pxq_llama engine, PXA_ENHANCE=1, fair-battle protocol (cold ~5.8k-token prompt, temp 0, median of 3).

File Tier bpw Size Fits
PXA-Fusion4-35B-PXQ6.gguf PXQ6 (real 5-bit) ~5.27 23.3 GB 24 GB card — top quality
PXA-Fusion4-35B-PXQ4.gguf PXQ4 ~4.27 19.3 GB flagship — recommended, 2×16 GB or one 24 GB
PXA-Fusion4-35B-PXQU16.gguf PXQ-Universal ~3.2 14.6 GB fills a 16 GB card
PXA-Fusion4-35B-PXQU12.gguf PXQ-Universal ~2.65 12.2 GB fills a 12 GB card
PXA-Fusion4-35B-PXQ2.gguf PXQ2 ~2.27 11.2 GB smallest — 11 GB cards
mmproj-fusion4-f16.gguf vision projector — 0.9 GB add for image input

Measured speed (t/s), PXQ4:

Cards Prefill Decode Decode + MTP
2× Tesla P100 (sm_60) 1,163 56.8 60.7 (accept ~0.68)
1× Tesla V100 (sm_70) 2,358 — 108.3
PXQ2, 1× P100 1,161 58.4 —
PXQ2, GTX 1080 Ti (ub 512) 855 61.6 —

Run it — exactly what we use

Get the pxq_llama engine (prebuilt release or build main), then:

llama-server -m PXA-Fusion4-35B-PXQ4.gguf \
  -c 73728 -ngl 99 -sm layer -fa on -ctk f16 -ctv f16 -b 2048 -ub 2048 \
  --jinja --chat-template-kwargs '{"enable_thinking":false}' \
  --temp 1.0 --top-p 0.95 --top-k 20 --min-p 0
# env: PXA_ENHANCE=1 auto-tunes per card. Optional: --spec-type mtp:n_max=1 (MTP), --mmproj mmproj-fusion4-f16.gguf (vision)

The template flags are required, not optional. --jinja + --chat-template-kwargs '{"enable_thinking":false}' select the correct chat template and no-think mode. Omitting them is the #1 cause of looping / rambling / hallucination — this is a Qwen-family model and it needs its template.

Sampling we serve with: --temp 1.0 --top-p 0.95 --top-k 20 --min-p 0 (tuned for multi-turn agent use). Running solo and want it more conservative? Use Qwen's official no-think set --temp 0.7 --top-p 0.8 --top-k 20 --min-p 0, and add --repeat-penalty 1.05 as a loop safety net.

Running an agentic / coding harness? Use these flags. They are not optional for agent work - they were derived from 144 interleaved measured runs, not guesswork.

llama-server -m PXA-Fusion4-35B-PXQ4.gguf --jinja \
  --reasoning off \
  --temp 0.7 --top-p 0.8 --top-k 20 --min-p 0 \
  --presence-penalty 1.5 --repeat-penalty 1.15 --repeat-last-n 256 --dry-multiplier 0.8 \
  -n 2048 -c 32768 -np 1 -ngl 99 -fa on
  • --reasoning off is the primary fix. The server default is --reasoning auto, which resolves to thinking ON, leaving every assistant turn starting inside an open <think> block with nothing to constrain it. Measured: 5/48 failures with thinking ON vs 0/72 with thinking OFF (Fisher p=0.0090).
  • The penalties are the brake. presence-penalty 1.5 is Qwen's own prescribed value for this model family; the other three are our PXQ1 repetition-guard preset, which does not auto-arm on other tiers. Verified not to break tool-calling (24/24 clean tool calls with penalties on).
  • -n 2048 is the belt. finish_reason currently reports "stop" even when generation is cut at the token cap, so a harness cannot detect a runaway. Cap it server-side.
  • Do NOT use --reasoning-budget 0. We measured it inert with this template - 24/24 runs still produced full-length reasoning. It will not save you.

Older build that rejects --reasoning? Use --chat-template-kwargs '{"enable_thinking":false}' instead.

Verify the flag actually applied before testing - the rendered prompt must end with a closed <think>\n\n</think>\n\n, not an open <think>\n:

curl -s http://127.0.0.1:8080/apply-template \
  -H "Content-Type: application/json" -d '{"messages":[{"role":"user","content":"hi"}]}'

Also make sure your client sends a real OpenAI tools array. Without one, the model emits its tool call as XML inside content, your harness sees an empty tool_calls, and it looks like the model did nothing. With the default reasoning_format=deepseek, prose goes to reasoning_content and content can be an empty string - read both.

License

Apache-2.0. Weights are a separate work from the pxq_llama engine (MIT). Base lineage: Qwen3.5-35B-A3B.

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