Darwin-35B-A3B-Opus

35B MoE (3B active) | GPQA Diamond 90.0% (Father 84.2%, Mother 85.0%) | MMMLU 85.0% | Multimodal | 201 Languages | 262K Context | 147.8 tok/s | Apache 2.0

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Technical Definitions

Before describing the methodology, we define the terms used throughout this document. These are not metaphors — they refer to specific, measurable quantities.

Term	Definition	Measurement
Model MRI	Layer-level profiling of expert activation patterns and layer importance	1K-sample calibration set, per-layer expert activation frequency, routing entropy, probe cosine distance
Dead Expert	A MoE expert rarely selected by the router	Activation frequency < 5% across calibration dataset
Routing Entropy	Shannon entropy of the router's softmax distribution	H = -sum(p_i * log2(p_i)). Healthy range for top-8-of-256: 3.0-4.5 bits
Expert Activation Frequency	Selection rate of each expert by the router	Count per expert across 1K samples, normalized to percentage
MRI-Guided Merge	Per-block merge ratios derived from parent diagnostics	Layers with high dead-expert counts get higher donor weight; healthy layers retain recipient weight
Health Check	Post-merge structural validation	Layer-by-layer importance comparison: child vs both parents. Flags interference or function loss
Golden Layer	Layer with highest measured importance for a target capability	Identified by peak probe cosine distance (e.g., L38 for reasoning)

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Benchmark Results

GPQA Diamond (198 Questions, Graduate-Level Reasoning)

Model	Accuracy	Multimodal	Architecture
Darwin-35B-A3B-Opus (Child)	90.0%	Image/Video	Qwen3.5-35B-A3B
Mother (Jackrong Claude 4.6 Opus Distilled)	85.0%	Text-only training	Qwen3.5-35B-A3B (same)
Father (Qwen3.5-35B-A3B Official)	84.2%	Image/Video	Qwen3.5-35B-A3B

Evaluation: SGLang, context 32768, temperature 0, greedy decoding, official GPQA prompt format

MMMLU (Multilingual Knowledge, 29 Languages)

Model	Accuracy
Darwin-35B-A3B-Opus (Child)	85.0%
Father (Qwen3.5-35B-A3B Official)	85.2%

• GPQA vs Father: +6.9% relative improvement
• GPQA vs Mother: +5.9% relative improvement
• MMMLU: Father-level multilingual knowledge preserved (85.0% vs 85.2%)

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Parent Models

Both parents share the identical Qwen3.5-35B-A3B architecture (40 layers, 256 experts, GDN+MoE hybrid). The Mother is a LoRA SFT on the same base — not a different architecture. "Text-only" refers to the training data (Claude 4.6 Opus reasoning chains), not the model structure.

Role	Model	Architecture	Training
Father	Qwen/Qwen3.5-35B-A3B	Qwen3.5-35B-A3B	Original pre-training + RLHF
Mother	Jackrong/Qwen3.5-35B-A3B-Claude-4.6-Opus-Reasoning-Distilled	Qwen3.5-35B-A3B (same)	LoRA SFT with text-only Claude reasoning chains

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Methodology: Darwin V5

Relationship to Existing Tools

Darwin V5 uses mergekit as its merge backend. We do not claim to have invented evolutionary merging — mergekit's evolve feature already provides this capability. What Darwin adds is a three-phase diagnostic pipeline that wraps mergekit with pre-merge profiling and post-merge verification.

Pipeline

Standard mergekit evolve:
  Random initial params --> Evolve --> Best score

Darwin V5:
  Phase 0: Profile both parents (40 layers x 256 experts)
      |    Measure: expert activation frequency, routing entropy,
      |    probe cosine distance per layer
      v
  Phase 1: Evolution with diagnostic-informed initial genome
      |    Search space constrained by dead expert map + layer importance
      v
  Phase 2: mergekit DARE-TIES merge + benchmark evaluation
      |    (same merge backend as standard mergekit)
      v
  Phase 3: Profile the child, compare against both parents
      |    Detect: interference, function loss, dead expert inheritance
      v
  Final model

What Darwin V5 Adds Over Standard mergekit evolve

Capability	mergekit evolve	Darwin V5
Merge backend	mergekit	mergekit (same)
Evolution algorithm	CMA-ES / random search	CMA-ES with diagnostic-informed initial population
Pre-merge parent analysis	None	Expert activation frequency, routing entropy, probe cosine distance across 40L x 256E
Initial search space	Full parameter space	Constrained by parent diagnostics
Dead expert awareness	None	Detects dead experts, adjusts density to compensate
Post-merge validation	Benchmark score only	Layer-by-layer child vs parents comparison
Failure diagnosis	"Score went down"	"L23 interference: child importance 2.3x parent, weight conflict at attention heads"

How Diagnostics Changed the Merge

Without diagnostics (V4 blind evolution):

• ratio=0.481, attn=0.168, ffn=0.841
• Uniform across all 40 layers

With diagnostics (V5):

• L0-L37: t=0.599 (Mother 60%), Mother's router
• L38: t=0.900 (Mother 90%), Mother's router — identified as reasoning core by probe cosine distance
• L39: t=0.534 (Father 47%), Father's router — preserves output/multimodal routing

The diagnostic profile identified L38 as having the highest cosine distance on REASONING and CODE probes. This informed the per-block strategy rather than relying on blind search to discover it.

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Parent Model Diagnostics

Mother: Expert Activation Analysis

Metric	Value	Interpretation
Router Entropy	~1.0 across all layers	Healthy — experts evenly distributed among active ones
Dead Expert %	50-65% in middle layers	LoRA SFT only updated parameter subsets; multimodal/multilingual experts became inactive
Expert Similarity	0.001-0.008	Healthy — surviving experts remain diverse

L34-L38 shows high cosine distance across REASONING, CODE, LOGIC probes — this is where the Claude distillation concentrated its reasoning patterns.

Father: Baseline Profile

The Father shows uniform expert activation across all 40 layers — all experts active. This makes it suitable as a donor for the Mother's inactive expert slots.

Parent Comparison

• Above zero: Father stronger — L0-L5 (embedding/early layers)
• Below zero: Mother stronger — L5-L35 consistent advantage
• L34-L38: Mother peaks on REASONING and CODE probes
• L39: Father recovers — output layer

This advantage map directly informed the 3-block merge recipe.

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Merge Configuration

# Darwin V5 diagnostic-guided layer-wise merge
# Method: DARE-TIES via mergekit
# Genome: ratio=0.800 attn=0.320 ffn=0.590 density=0.799

L0-L37:  t=0.5988 (Mother 60%) — router from Mother
L38:     t=0.9000 (Mother 90%) — reasoning core
L39:     t=0.5336 (Father 47%) — router from Father (output routing)

Parameter	V4 (Blind)	V5 (Guided)	Rationale
global_ratio	0.481	0.800	Mother weight increased — diagnostics confirmed her reasoning layers are high quality
attn_ratio	0.168	0.320	More Mother attention — probe data showed reasoning concentration in attention patterns
ffn_ratio	0.841	0.590	More conservative — Father's FFN experts fill dead slots
density_b	0.971	0.799	Reduced — compensates for Mother's 50-65% dead experts

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Post-Merge Health Check

Layer-by-layer importance comparison between the child and both parents:

• Layer 0 (Embedding): Child 0.42, parents 0.35-0.50. No interference.
• Layers 1-33: Near-zero across all three. Normal for MoE middle layers.
• Layers 34-39: Importance rises. Child matches or exceeds parents — reasoning transfer confirmed.
• Layer 39 (Output): Child 0.48, matching parents. Output intact.

No interference detected. No function loss detected.

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Inherited Capabilities

From Father (Qwen3.5-35B-A3B):

• Multimodal: Image and video understanding
• 201 Languages: Multilingual coverage
• 262K Context: Native long-context (extendable to 1M via YaRN)
• Gated DeltaNet + MoE architecture
• Multi-Token Prediction

From Mother (Claude 4.6 Opus Distilled):

• Structured step-by-step reasoning within <think> tags
• Coding agent compatibility
• Tool calling stability

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Performance

Metric	Value
Generation Speed	147.8 tok/s
Environment	Single NVIDIA H100 93GB NVL, SGLang, BF16

Setup	VRAM	Status
BF16 Full Precision	65.5 GiB
Single H100 93GB	93 GB	Comfortable
Single A100 80GB	80 GB	Tight
Q4_K_M Quantized	~18 GiB
Single RTX 4090 24GB	24 GB	Comfortable

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Model Specifications

Architecture	Qwen3.5 MoE (Gated DeltaNet + MoE)
Total Parameters	35B
Active Parameters	3B per forward pass
Layers	40
Layout	10 x (3 x GDN-MoE + 1 x Attention-MoE)
Experts	256 (8 routed + 1 shared active)
Context Length	262,144 native
Languages	201
Multimodal	Image and Video
License	Apache 2.0

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Usage

SGLang (Recommended)

python -m sglang.launch_server \
  --model-path FINAL-Bench/Darwin-35B-A3B-Opus \
  --tp 1 \
  --mem-fraction-static 0.90 \
  --context-length 32768 \
  --trust-remote-code

vLLM

vllm serve FINAL-Bench/Darwin-35B-A3B-Opus \
  --trust-remote-code \
  --enforce-eager

Transformers

from transformers import AutoTokenizer, AutoModelForCausalLM

tokenizer = AutoTokenizer.from_pretrained(
    "FINAL-Bench/Darwin-35B-A3B-Opus",
    trust_remote_code=True,
    use_fast=True,
)
model = AutoModelForCausalLM.from_pretrained(
    "FINAL-Bench/Darwin-35B-A3B-Opus",
    dtype="bfloat16",
    device_map="auto",
    trust_remote_code=True,
)

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Evolution Details

Engine	Darwin V5 (Evolutionary Merge + Layer-Level Diagnostics)
Merge Backend	mergekit (DARE-TIES)
Evolution	CMA-ES, Phase 1 (200 steps proxy) + Phase 2 (30 steps real benchmark)
Final real_score	0.8405
Merge Time	181.6 seconds
Merge Commit	109838c2
Infrastructure	4 x NVIDIA H100 93GB NVL

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Acknowledgements

• Korean Government — GPU Support Program research grant
• Qwen Team — Qwen3.5-35B-A3B base architecture
• Jackrong — Claude 4.6 Opus Reasoning Distilled model
• mergekit — Merge backend infrastructure
• nohurry, TeichAI — Distillation datasets

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Citation

@misc{vidraft_darwin_35b_opus,
  title        = {Darwin-35B-A3B-Opus: Diagnostic-Guided Evolutionary Merge},
  author       = {VIDRAFT},
  year         = {2026},
  publisher    = {Hugging Face},
  howpublished = {\url{https://huggingface.co/FINAL-Bench/Darwin-35B-A3B-Opus}}
}

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FAQ

How does Darwin V5 differ from mergekit evolve?

Darwin V5 uses mergekit as its merge backend. The addition is a three-phase diagnostic pipeline: (1) pre-merge parent profiling measuring expert activation frequency, routing entropy, and probe cosine distance across 40 layers x 256 experts, (2) evolution with diagnostic-informed initial population and constrained search space, (3) post-merge child validation comparing layer importance against both parents. Standard mergekit evolve does not include phases 1 and 3.

What are "Dead Experts"?

In MoE models, each layer has 256 experts. An expert is "dead" when its activation frequency falls below 5% across a 1K-sample calibration dataset. The Mother showed 50-65% dead experts because LoRA SFT only updates a parameter subset — experts not activated by text-only training data become inactive.

Are both parents the same architecture?

Yes. Both are Qwen3.5-35B-A3B — identical architecture, layer count, and expert structure. The Mother is a LoRA SFT on the same base. "Text-only" refers to training data, not model architecture.

What GPU do I need?

BF16: H100 93GB (comfortable) or A100 80GB (tight). Q4: RTX 4090 24GB. Only 3B active per token despite 35B total.

Does it support images/video?

Yes. Inherited from the Father. The Mother lost multimodal during text-only fine-tuning, but the merge preserves Father's multimodal routing at L39 and replaces dead multimodal experts with living ones.