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.

---

🧬 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

---

📊 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

Single domain, random folds. The ladder under the harder leaderboard protocol reads 0.7272 / 0.7289 / 0.6506 / 0.6360 — see the section below.

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

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📊 Independent leaderboard — 2,018 items, leave-one-domain-out

The Typed Decision Leaderboard scores answer verifiers from several vendors on one identical item set with identical labels: https://huggingface.co/spaces/mayafree/typed-decision-leaderboard

System	AUC
Darwin-397B-ZTC	0.7272
JEV (TypeSafe AI)	0.7350
ZTC-Judge-27B	0.7289
GPT-5.2 asked directly	0.7148
open-jev 4B	0.6844
Answer length and formatting only	0.6223

Revised 2026-09-21. Earlier revisions of this card reported 0.7364 for Darwin-397B-ZTC and 0.7282 for ZTC-Judge-27B. Those figures were produced by a run whose standardisation statistics were computed over all five domains, including the held-out one, which leaks a small amount of the evaluation domain into every figure. Re-run with the statistics fitted inside the training domains only, the figures are 0.7272 and 0.7289. Cite the current values.

| Patronus Lynx 8B | 0.5179 | | The answering model's own stated confidence | 0.5000 |

First place — and the gap to second is 0.0014, with a 95% interval of −0.019 to +0.032. Under the board's own rule an interval containing zero yields no rank, so this model and JEV are not statistically separable. That is stated here for the same reason it is stated there.

Per domain, against the surface baseline in the same domain:

Domain	Baseline	Darwin-397B-ZTC	ZTC-Judge-27B
Professional exams (law · math · biology)	0.7138	0.8660	0.8462
Biology & medicine	0.5908	0.7433	0.7154
Disaster & safety procedures	0.5949	0.7319	0.6961
Scientific reasoning	0.7272	0.6287	0.7410
General multi-step reasoning	0.5420	0.6072	0.6172
Size-weighted mean	0.6223	0.7272	0.7289

🔴 On scientific reasoning the 27B model beats this one by 0.11. A model fourteen times smaller wins that column. It is printed rather than dropped, because the ladder only means something if the places it inverts are visible.

Self-readout. Given only the question, this model answers on its own and the same forward pass tells whether it was right: 0.7572 (3 domains, 1,595 items). Verifiers that see only text from outside a model cannot do this at all.

Protocol. Every figure comes from a domain the probe never saw; hyper-parameters are selected inside the training domains only; scores are computed per domain and then size-weighted. Pooling all items into a single AUC inflates the result, because score scales differ between domains.

---

Known limitation — the answering-model mixture matters

• Sensitive to which model wrote the answer. The probe is fitted on answers from four models. Adding 1,772 answers from a single additional model shifted the mixture and lowered the size-weighted score from 0.7278 to 0.7177 — professional exams rose to 0.8575 while every other domain fell. Treat "works on any model's output" as a design goal, not a measured guarantee: if your generator differs sharply from the training mixture, measure before relying on the number.

🔎 Two measurements, two protocols — do not mix them

	Section above (PubMedQA / KMMLU)	Leaderboard
Items	539 self-judged · 400 other-judged	2,018, five domains
Split	random folds	held-out domain
Result	0.8801 · 0.8228	0.7272

Leave-one-domain-out is far harsher than random folds, which is why the numbers differ. Quote 0.7272 when comparing against other systems; the higher figures describe an easier protocol.

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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

---

🏆 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.

---

API — drop-in for an existing JEV integration

The endpoint takes the same request shape and returns the same response shape, so switching an existing integration is a URL change.

POST /v1/evaluate
Authorization: Bearer <token>

{"model": "vidraft/ztc",
 "state": {"question": "...", "answer": "..."},
 "questions": {"correct": {"type": "boolean",
                           "instructions": "Is the ANSWER factually correct?"}}}

{"model": "vidraft/ztc-judge-397b",
 "answers": {"correct": {
    "probability": 0.1043,
    "verdict": "review",
    "score": -0.72,
    "position": 0.268,

    "band": "low",
    "action": "hold_or_escalate",
    "measured": {
      "band_accuracy": 0.485,
      "base_accuracy": 0.748,
      "if_lowest_20pct_dropped": 0.814,
      "escalate_gain_at_20pct_budget": 0.0134,
      "do_not": "resample_same_model",
      "why_not": "measured: fixes 6.7% of wrong answers, breaks 13.1% of right ones"}}},
 "usage": {"generated_tokens": 0}}

type accepts boolean and noul. Existing clients read answers.<key>.probability and ignore the rest; the additional fields are there for clients that want to act on the score rather than merely record it. 0.19 s per call, zero generated tokens.

What probability means

The raw score is unbounded. The shipped calibration maps it to P(answer is correct), fitted leave-one-domain-out — the mapping never sees the domain it is applied to.

	Expected calibration error
ZTC-Judge-27B (after calibration)	0.0245
JEV, as shipped	0.0381
JEV, after the same calibration	0.0261
Laya-Multilingual, as shipped	0.4985
Laya-Typed-Decisions, as shipped	0.2641

Measured on the same 2,018 items. ZTC and JEV are effectively tied on calibration; the difference of 0.0016 is not meaningful. Figures published elsewhere for these systems were measured on other test sets and do not reproduce here.

🔴 Calibration is uneven across domains: 0.0225 on biology & medicine, but 0.2941 on scientific reasoning and 0.2381 on general reasoning. Treat the probability as reliable in the first case and as a ranking signal only in the other two.

What to do when the score is low

The score alone is not actionable, so the response carries the measured consequence of each choice.

Band	Share	Actual accuracy of answers in this band	Recommended
low	20%	48.5%	hold, or escalate to a stronger model
mid	40%	73.2%	escalate if budget allows
high	40%	89.6%	accept

Three things that work, measured on 2,018 items:

Action	Effect
Drop the lowest-scoring 20%	accuracy of what remains: 74.8% → 81.4%
Escalate the lowest 20% to a stronger model	+1.34 pp end-to-end
Send the lowest 20% to human review	catches 47.2% of all errors — 2.4× random

Generate several candidates and let the verifier pick

When the score is low, the most effective next step is not to escalate — it is to produce more candidate answers and select between them. Measured on 346 questions with five candidates each (1,730 candidates), all scored through this endpoint:

Policy	Accuracy	Output tokens	vs. one attempt
One attempt	49.13%	72	—
Majority vote over 3	46.82%	212	−2.31 pp
Majority vote over 5	46.53%	353	−2.60 pp
Pick best of 5 with this model	51.45%	353	+2.31 pp
Pick best of 5 with JEV	53.47%	353	+4.34 pp
Pick one of 5 at random	46.82%	353	−2.31 pp
Oracle — any correct candidate counts	63.87%	353	+14.74 pp

The same five candidates swing by 5 points depending on how one is chosen. Majority voting is worse than not resampling at all: when a model prefers a wrong answer, more samples make that wrong consensus more certain. A verifier that ranks the candidates is what turns extra samples into accuracy.

Spend the budget only where it is needed. Generating extra candidates only for low-scoring first attempts captures most of the gain at a fraction of the cost:

Triggered on	Accuracy	Output tokens	vs. one attempt
10% of items	49.71%	80	+0.58 pp
30% of items	50.87%	132	+1.73 pp
100% of items	51.45%	353	+2.31 pp

At a 30% trigger rate you get three quarters of the benefit for 1.8× the tokens, where always generating costs 4.9× for 1.3× the benefit.

Scope: one generator (GPT-4o-mini), one item set, five candidates. The oracle row shows the headroom that remains — a correct candidate is present far more often than any policy recovers it.

One thing that does not work:

🔴 Do not take a majority vote over resamples. Measured: five resamples with majority voting score 46.53% where a single attempt scores 49.13%. More candidates make a wrong consensus more certain unless something picks between them — see the table above.

Escalation pays for itself through precision, not recall. Re-answering repairs about 38% of wrong answers and damages about 30% of right ones, so a gate is only worth its budget if it mostly calls answers that are actually wrong.

---

⚙️ 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

---

🚀 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

---

🎯 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}
}