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AmanPriyanshu/
gpt-oss-17.9b-specialized-math-pruned-moe-only-27-experts

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Math GPT-OSS Model (27 Experts)

Project: https://amanpriyanshu.github.io/GPT-OSS-MoE-ExpertFingerprinting/

👥 Follow the Authors

Aman Priyanshu

Supriti Vijay

Introduction

This is a pruned variant of OpenAI's GPT-OSS-20B model, reduced to 27 experts per layer based on activation patterns from the AmanPriyanshu/GPT-OSS-20B MoE Expert Activations dataset. We analyzed router decisions across evaluation benchmarks to identify and retain experts most relevant for math tasks.

⚠️ Experimental Model: This is an experimental pruned model that may not work well - check the examples below to see if the outputs meet your needs before use.

This pruning approach reduces the model size while attempting to preserve performance on the target domain.

Model Architecture & Statistics

Metric	Value
Base Model	openai/gpt-oss-20b
Architecture	Mixture-of-Experts Transformer
Total Parameters	~17.9B (pruned from 21B)
Original Experts per Layer	32
Pruned Experts per Layer	27
Layers	24
Top-k Routing	4
Context Length	128K tokens
Attention Heads	64 (Query), 8 (Key-Value)
Residual Dimension	2880
Attention Pattern	Alternating dense & sliding window (128 tokens)
Positional Encoding	RoPE (Rotary Position Embedding)
Normalization	RMSNorm
Precision	BF16
License	Apache 2.0
Specialization	Math

Pruning Methodology

What is Expert Pruning?

Mixture-of-Experts models contain multiple specialized sub-networks (experts) per layer. During inference, only a subset of experts are activated for each token. Expert pruning involves:

Analyzing Usage Patterns: Tracking which experts activate most frequently for specific tasks
Removing Underutilized Experts: Discarding experts with low activation rates for the target domain
Preserving Router Functionality: Maintaining the routing mechanism with fewer available experts

Our Approach

Data-Driven Selection: Used activation patterns from math evaluation tasks
Systematic Reduction: Reduced from 32 to 27 experts per layer
No Retraining: Direct removal without additional training steps

Performance & Applications

Pruning Benefits

Smaller Memory Footprint: 84.4% of original expert parameters
Reduced Computational Load: Fewer routing decisions during inference
Focused Capabilities: Retains experts relevant to math tasks

Use Cases

Speculative Decoding: Draft model for full GPT-OSS-20B
Resource-Constrained Deployment: Edge devices, mobile applications
Research: Study expert specialization in MoE models
Fine-tuning: Smaller base model for domain adaptation

Note: Performance may vary depending on how well the pruned experts match your specific use case.

Motivation & Expert Selection

This mathematics-focused model utilizes experts that exhibited strong performance on mathematical reasoning tasks from MMLU mathematics subjects and quantitative sections. These experts excel at mathematical computation, proof strategies, and logical reasoning.

The expert selection process utilized our comprehensive analysis of router activation patterns across multiple evaluation benchmarks:

GPQA: Graduate-level questions in physics, chemistry, biology (Diamond & Expert subsets)
MMLU/MMLU-Pro: Comprehensive knowledge across 57+ subjects including science, medicine, law
SORRY-Bench: Safety evaluation across harmful content categories
Tulu3: Persona-driven instruction following with verifiable constraints
Polyglot-or-Not: Multilingual factual completion tasks

By identifying experts that consistently activated for math tasks, we created this specialized model that maintains domain expertise while significantly reducing computational requirements from 32 to 27 experts per layer.

Dataset & Analysis Foundation

This model is based on analysis from the GPT-OSS-20B MoE Expert Activations dataset available at: 🔗 https://huggingface.co/datasets/AmanPriyanshu/GPT-OSS-20B-MoE-expert-activations

The dataset contains router activation patterns from OpenAI's GPT-OSS-20B model across diverse evaluation benchmarks, enabling the creation of these domain-optimized models through systematic expert pruning.

Pruning Methodology

Our approach involves:

Activation Analysis: Comprehensive evaluation of expert usage patterns across domain-specific tasks
Expert Ranking: Identification of the most frequently activated experts for target domains
Systematic Pruning: Reduction from 32 to 27 experts while preserving router functionality
Quality Validation: Testing to ensure maintained performance on target tasks

This is a direct pruning approach - no additional training was performed. The model inherits all capabilities from the original GPT-OSS-20B with focused expert selection.

Usage

CPU Inference

python

from transformers import AutoModelForCausalLM, AutoTokenizer
import torch

# Load the specialized model on CPU
model = AutoModelForCausalLM.from_pretrained(
    "AmanPriyanshu/gpt-oss-17.9b-specialized-math-pruned-moe-only-27-experts", 
    torch_dtype=torch.bfloat16, 
    device_map="cpu", 
    trust_remote_code=True
)
tokenizer = AutoTokenizer.from_pretrained("AmanPriyanshu/gpt-oss-17.9b-specialized-math-pruned-moe-only-27-experts")

# Generate with the model
messages = [
    {"role": "user", "content": "Solve this equation: 2x + 5 = 17. Show your work step by step."}
]

inputs = tokenizer.apply_chat_template(
    messages, 
    add_generation_prompt=True, 
    return_tensors="pt", 
    return_dict=True,
    reasoning_effort="medium"
)

# Ensure inputs are on the same device as model
inputs = {k: v.to(model.device) for k, v in inputs.items()}

outputs = model.generate(
    **inputs, 
    max_new_tokens=512,
    do_sample=True,
    temperature=0.1,
    top_p=0.9,
    pad_token_id=tokenizer.eos_token_id,
    eos_token_id=tokenizer.eos_token_id
)

# Decode only the generated part
input_length = inputs['input_ids'].shape[1]
response_tokens = outputs[0][input_length:]
response = tokenizer.decode(response_tokens, skip_special_tokens=True)
print(response)

Apple Silicon (MPS) Inference

python

from transformers import AutoModelForCausalLM, AutoTokenizer
import torch

# Check MPS availability and load model
device = "mps" if torch.backends.mps.is_available() else "cpu"

model = AutoModelForCausalLM.from_pretrained(
    "AmanPriyanshu/gpt-oss-17.9b-specialized-math-pruned-moe-only-27-experts", 
    torch_dtype=torch.float16,  # Better MPS compatibility
    device_map=device, 
    trust_remote_code=True,
    low_cpu_mem_usage=True
)
tokenizer = AutoTokenizer.from_pretrained("AmanPriyanshu/gpt-oss-17.9b-specialized-math-pruned-moe-only-27-experts")

# Generate with the model
messages = [
    {"role": "user", "content": "Solve this equation: 2x + 5 = 17. Show your work step by step."}
]

inputs = tokenizer.apply_chat_template(
    messages, 
    add_generation_prompt=True, 
    return_tensors="pt", 
    return_dict=True,
    reasoning_effort="medium"
)

# Move inputs to model device
inputs = {k: v.to(model.device) if isinstance(v, torch.Tensor) else v for k, v in inputs.items()}

# Use torch.no_grad for MPS stability
with torch.no_grad():
    outputs = model.generate(
        **inputs, 
        max_new_tokens=512,
        do_sample=True,
        temperature=0.1,
        top_p=0.9,
        pad_token_id=tokenizer.eos_token_id,
        eos_token_id=tokenizer.eos_token_id,
        use_cache=True
    )

# Decode only the generated part
input_length = inputs['input_ids'].shape[1]
response_tokens = outputs[0][input_length:]
response = tokenizer.decode(response_tokens, skip_special_tokens=True)
print(response)

GPU Inference

For CUDA GPU inference, the models work with minimal modifications from the CPU example above. Simply change:

python

device_map="auto"  # Will automatically use GPU if available
torch_dtype=torch.bfloat16  # or torch.float16

Model Examples

The following examples demonstrate the model's performance on math tasks:

Example 1

Question: Solve this equation: 2x + 5 = 17. Show your work step by step.

Response:

<|channel|>analysis<|message|>Just solve linear.<|end|><|start|>assistant<|channel|>final<|message|>Sure! Let’s solve the equation step by step.

**Equation**

\[
2x + 5 = 17
\]

---

### 1. Isolate the term with \(x\)

We want the expression \(2x\) by itself on one side.  
Subtract \(5\) from both sides of the equation:

\[
2x + 5 - 5 = 17 - 5
\]

\[
2x = 12
\]

---

### 2. Solve for \(x\)

Now divide both sides by the coefficient of \(x\), which is \(2\):

\[
\frac{2x}{2} = \frac{12}{2}
\]

\[
x = 6
\]

---

### 3. Check the solution

Plug \(x = 6\) back into the original equation to verify:

\[
2(6) + 5 = 12 + 5 = 17
\]

The left‑hand side equals the right‑hand side, so the solution is correct.

---

**Answer**

\[
\boxed{x = 6}
\]<|return|>

Example 2

Question: What is the Pythagorean theorem and how is it used?

Response:

<|channel|>analysis<|message|>Need explain theorem, formula, usage.<|end|><|start|>assistant<|channel|>final<|message|>**The Pythagorean Theorem**

> In a right‑angled triangle, the square of the length of the hypotenuse (the side opposite the right angle) equals the sum of the squares of the lengths of the other two sides.

Mathematically:

\[
c^2 = a^2 + b^2
\]

where  
- \(c\) = length of the hypotenuse,  
- \(a\) and \(b\) = lengths of the two legs.

---

### How It Is Used

| Context | What you do | Example |
|---------|-------------|---------|
| **Geometry** | Find a missing side of a right triangle | If \(a = 3\) m and \(b = 4\) m, then \(c = \sqrt{3^2+4^2}=5\) m. |
| **Construction & Engineering** | Verify right angles or measure distances | A carpenter checks that a corner is 90° by measuring the diagonal of a square cut‑out. |
| **Navigation & Surveying** | Compute straight‑line distances (great‑circle approximations, planar maps) | A surveyor uses the theorem to find the distance between two points when the east‑west and north‑south offsets are known. |
| **Computer Graphics** | Calculate Euclidean distances between points | In 2‑D or 3‑D space, the distance between \((x_1,y_1)\) and \((x_2,y_2)\) is \(\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}\). |
| **Physics** | Resolve vectors into components | The magnitude of a velocity vector \(\vec{v} = (v_x, v_y)\) is \(|\vec{v}| = \sqrt{v_x^2+v_y^2}\). |
| **Computer Science** | Algorithms for nearest‑neighbor search, clustering, etc. | K‑means clustering uses Euclidean distance to assign points to centroids. |
| **Art & Design** | Create perspective drawings, calculate proportions | An artist uses the theorem to maintain correct proportions when drawing a 3‑D object on 2‑D paper. |

---

### Quick “Check‑It” Formula

If you know two sides, you can find the third:

Example 3

Question: Calculate the area of a circle with radius 7 meters.

Response:

<|channel|>analysis<|message|>Compute area = π r^2 = π*49 ≈ 153.938.<|end|><|start|>assistant<|channel|>final<|message|>The area \(A\) of a circle is given by

\[
A = \pi r^{2}
\]

where \(r\) is the radius.

For a radius of \(7\) m:

\[
A = \pi (7\,\text{m})^{2} = \pi \times 49\,\text{m}^{2}
\]

\[
A \approx 3.14159 \times 49 \;\text{m}^{2} \approx 153.94 \;\text{m}^{2}
\]

So the area of the circle is **about \(154\ \text{m}^2\)** (rounded to the nearest whole square meter).<|return|>

Citation

If you use this model in your research, please cite:

bibtex

@misc{priyanshu2025gptoss,
  title={{GPT-OSS MoE Expert Fingerprinting: Analyzing Expert Activation Patterns in Mixture of Experts Models}},
  author={Priyanshu, Aman and Vijay, Supriti},
  year={2025},
  howpublished={\url{https://amanpriyanshu.github.io/GPT-OSS-MoE-ExpertFingerprinting/}},
  note={Interactive analysis tool for expert activation patterns in MoE architectures}
}

References & Resources

Original Model: OpenAI GPT-OSS Model Card
Model Hub: GPT-OSS-20B on Hugging Face
Expert Analysis Dataset: GPT-OSS-20B MoE Expert Activations
Project Page: GPT-OSS MoE Expert Fingerprinting
GitHub Repository: OpenAI GPT-OSS