ZTC ecosystem

Zero-Token Confidence (ZTC) reads a model's own internal state to judge whether an answer is right — generating zero tokens. Darwin-397B-ZTC ships a self-readout probe; ZTC-Judge-27B judges other models' answers; the arcade shows the gate deciding execute or hold in real time.

Darwin-397B-ZTC

397B Mixture-of-Experts built on Qwen 3.5 · FP8 · GPQA Diamond 93.43 % · ZTC on board

reasoning · MoE · FP8 · 262K long context · Korean + English · hallucination detection · tool calling

Half the footprint, GPQA Diamond 93.43 %. And this model stops itself before it acts on an answer it is about to get wrong.

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🧬 The Darwin Family

Darwin is VIDRAFT's measurement-driven reasoning model family — roughly 20 official models, 400+ community derivatives, and a standing place among the top open models on GPQA.

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🧬 Darwin — transplanting the experts that work

A large MoE model is made of hundreds of experts. Darwin V9 selects the experts that perform best across several high-performing models, transplants them onto a base backbone, and fuses them with trust-weighted evolutionary merging.

Nothing is trained from scratch — proven capability is grafted on. That is why the same method holds across every model size.

Model	Scale	GPQA Diamond
Darwin-9B-NEG	9B	84.3
Darwin-27B-Opus	27B dense	86.9
Darwin-36B-Opus	36B MoE	88.4
Darwin-28B-Opus	28B	88.89
Darwin-28B-REASON	28B + DELPHI	89.39
Darwin-398B-JGOS	397B MoE (bf16)	90.9
Darwin-397B-ZTC	397B MoE (FP8)	93.43

Lineage

Role
Base	Qwen/Qwen3.5-397B-A17B	397B MoE backbone, ~17B active — Apache-2.0
Darwin V9	expert transplant + trust-weighted evolutionary merging	this is where the model becomes Darwin
Precision	compressed-tensors W8A8 FP8	418.7 GB
ZTC	zero-token confidence readout	ships in ztc/

• Darwin V9 — evolutionary FFN/expert transplant and trust-weighted merging onto large MoE backbones
• FINAL Bench — VIDRAFT's evaluation framework
• Four-layer Pre-AGI roadmap — Darwin → AETHER → PROMETHEUS → HEPHAESTUS

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🏛️ ZTC — it knows before it answers

Until now there were two ways to find out whether a model is about to be wrong. Both of them only work after the answer already exists.

Existing approach	Limitation
Ask the model in words	Costs extra tokens, adds latency, and models are badly overconfident
Attach an external judge model	Two models to operate · re-reads the entire answer · degrades on long outputs · 🔴 arrives too late — the answer is already produced

ZTC is a third path. It reads the model's own internal state once, before generation begins.

	External judge model	ZTC
When	After the answer	Before it starts
Extra model	Required (two to operate)	None (one)
Extra generated tokens	Re-processes prompt + answer	0
Added latency	A second inference pass	0.52 ms — 0.003 % of generation cost
Long answers, long trajectories	Degrades as length grows	Length-independent

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📊 Measured — on this model

① It judges its own answers (PubMedQA, 539 items, 146 incorrect)

	AUROC
Self-reported confidence (asked in words)	0.7646
ZTC (internal-state readout)	0.8801
Gain	+0.1155

Permutation null control: z = 13.31 — shuffle the labels and the signal disappears.

② It judges other models' answers (Korean KMMLU, 400 items — law, math, biology, history)

Judge	AUROC
Darwin-397B-ZTC	0.8228 (z = 9.66)
Qwen3.5-27B	0.8171
Qwen3.5-9B	0.7297
Qwen3.5-4B	0.7284
Open-source 4B judge model	0.6844

Same 400 items, same conditions: +0.138 over the open-source judge model.

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📦 The probe ships with this model

File
ztc/ztc_probe_darwin397b.npz	45 KB — the confidence readout for this model
ztc/usage.py	minimal, runnable example

z = np.load("ztc/ztc_probe_darwin397b.npz")
s = ((h - z["mu"]) / z["sd"]) @ z["w"]        # h = last-token hidden state, 4096-dim
p = 1 / (1 + np.exp(-(z["cal_A"] * (s - z["s_mean"]) / z["s_std"] + z["cal_B"])))

One matrix product. No second model, no extra tokens, no network call. The probe is specific to this model's hidden space (4096-dim) and does not transfer to others.

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🤖 Why this is decisive for agents — after-the-fact report vs. pre-action stop

In an agent loop the expensive thing is not tokens. It is actions. Files get edited, APIs get called, payments go through, mail leaves the building.

External judge :  [generate] → [tool runs] → [cost, time, side effects] → [judge] → "that was wrong"
ZTC            :  [read state, 0.52 ms] → stop here if risky → the action never happens

In front of an irreversible action, an after-the-fact verdict is an incident report.

Patterns

Pattern	Behaviour
Tool-call gating	Low confidence → do not call the tool, ask a human instead
Model routing	Send only the low-confidence queries to a larger model or external API
Retry budgeting	Spend multi-sample decoding only on the steps that wobble
Long-trajectory monitoring	Agent trajectories run to tens of thousands of tokens — length-independent, so it can stay on at every step
Selective prediction	Withhold a risky answer and return "I don't know"

Gate deployment, measured

Metric	Before	After
Gate accuracy	71.3 %	93.3 %
Incorrect answers blocked	40.7 %	74.1 %
Expensive-path calls	42 %	17 %

At effectively zero cost it can stay on for every request.

Use cases — hallucination detection · uncertainty quantification · confidence calibration · selective prediction · routing risky queries upstream · pre-action gating for agents

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🏆 GPQA Diamond 93.43 %

Model	GPQA Diamond
Darwin-397B-ZTC	93.43
GPT5.2	92.4
Gemini-3 Pro	91.9
Qwen3.5-397B-A17B	88.4
Claude 4.5 Opus	87.0

GPQA Diamond, all 198 items · greedy · single sample · no test-time engine

Comparison figures: Qwen3.5-397B-A17B official model card.

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⚙️ Specifications

Item	Value
Architecture	Qwen3_5MoeForConditionalGeneration
Parameters	397 B total / 17 B active (512 experts, 10 routed + 1 shared per token)
Layers · hidden	60 · 4096
Attention	Hybrid (45 linear + 15 full attention layers)
Precision	FP8 (compressed-tensors W8A8)
Size on disk	418.7 GB
Context	262,144 tokens
License	apache-2.0

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🚀 Quickstart

Serving with vLLM (4 × H100 80GB)

vllm serve FINAL-Bench/Darwin-397B-ZTC \
  --served-model-name darwin-397b \
  --tensor-parallel-size 1 --pipeline-parallel-size 4 \
  --gpu-memory-utilization 0.92 --max-model-len 262144 \
  --cpu-offload-gb 20 --enforce-eager --trust-remote-code \
  --reasoning-parser qwen3 --enable-auto-tool-choice \
  --port 8000

SGLang

python -m sglang.launch_server --model-path FINAL-Bench/Darwin-397B-ZTC \
  --port 8000 --tp-size 8 --context-length 262144

Chat Completions (OpenAI-compatible)

from openai import OpenAI
c = OpenAI(base_url="http://localhost:8000/v1", api_key="EMPTY")

r = c.chat.completions.create(
    model="darwin-397b",
    messages=[{"role": "user", "content": "Why is the Riemann hypothesis hard?"}],
    temperature=0.0, max_tokens=8192,
)
m = r.choices[0].message
print(m.reasoning_content)   # thinking trace
print(m.content)             # final answer

🛠️ Tool calling

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Get the current weather for a city",
        "parameters": {"type": "object",
                       "properties": {"city": {"type": "string"}},
                       "required": ["city"]},
    },
}]

r = c.chat.completions.create(
    model="darwin-397b", tools=tools,
    messages=[{"role": "user", "content": "What's the weather in Paris?"}],
)
print(r.choices[0].message.tool_calls)

🤖 Agents and coding CLIs

The endpoint is OpenAI-compatible, so existing tooling connects unchanged.

opencode — ~/.config/opencode/opencode.json

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "darwin": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "Darwin (local)",
      "options": { "baseURL": "http://localhost:8000/v1", "apiKey": "EMPTY" },
      "models": { "darwin-397b": { "name": "Darwin-397B-ZTC" } }
    }
  }
}

Any OpenAI-compatible client (Cline, Continue, Aider, …)

export OPENAI_BASE_URL=http://localhost:8000/v1
export OPENAI_API_KEY=EMPTY
export OPENAI_MODEL=darwin-397b

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🎯 Intended use

• Graduate-level STEM reasoning (GPQA, science qualifying exams)
• Mathematics and long multi-step chains of thought
• Code generation and debugging
• 🤖 Agent workflows — ZTC blocks irreversible tool calls before they run
• Bilingual Korean + English reasoning (Chinese and Japanese supported)
• Work where a wrong answer is expensive — ZTC filters risky answers before they ship

🔗 Links

• 🌐 vidraft.net — VIDRAFT
• 🤗 FINAL-Bench — all models
• 📱 POCKET — on-device line that runs on phones and GPU-less PCs

📚 Citation

@misc{darwin397b_ztc_2026,
  title = {Darwin-397B-ZTC: FP8 Mixture-of-Experts with Zero-Token Confidence},
  year  = {2026},
  url   = {https://vidraft.net},
  note  = {Base: Qwen/Qwen3.5-397B-A17B}
}