from transformers import AutoModelForCausalLM, AutoTokenizer

model = AutoModelForCausalLM.from_pretrained(
    "khadim-hussain/gpt-oss-20b-stem-reasoning-merged",
    torch_dtype="auto",
    device_map="auto",
    trust_remote_code=True,
)
tokenizer = AutoTokenizer.from_pretrained(
    "khadim-hussain/gpt-oss-20b-stem-reasoning-merged",
    trust_remote_code=True,
)

# GPT-OSS uses Harmony format
prompt = """<|start|>system<|message|>You are a helpful assistant trained by OpenAI.

Reasoning: medium

# Valid channels: analysis, commentary, final. Channel must be included for every message.<|end|><|start|>user<|message|>What is DNA?<|end|><|start|>assistant"""

inputs = tokenizer(prompt, return_tensors="pt").to(model.device)
outputs = model.generate(**inputs, max_new_tokens=512)
print(tokenizer.decode(outputs[0], skip_special_tokens=False))

Model Details

Property	Value
Base Model	openai/gpt-oss-20b
Type	Merged (LoRA merged into base weights)
Size	~41GB (bf16)
Parameters	21B total, 3.6B active (MoE)
Format	OpenAI Harmony
Training	QLoRA fine-tuning on STEM Q&A dataset

Harmony Response Format

GPT-OSS uses the OpenAI Harmony format with channels:

<|channel|>analysis - Chain-of-thought reasoning (thinking)
<|channel|>final - Final user-facing response

Example output:

<|start|>assistant<|channel|>analysis<|message|>DNA stands for deoxyribonucleic acid. It is a molecule...<|end|>
<|start|>assistant<|channel|>final<|message|>DNA is a molecule that carries genetic instructions used in growth, development, and reproduction.<|return|>

Training Metrics

Metric	Value
Train Loss	1.087
Eval Loss	0.837
Training Examples	4,260
Evaluation Examples	474
Epochs	1

GGUF Version

A GGUF quantized version (Q8_0, ~21GB) is available for use with Ollama/llama.cpp:

bash

# Using Ollama
ollama run khadim-hussain/gpt-oss-20b-stem-reasoning

See: khadim-hussain/gpt-oss-20b-stem-reasoning-GGUF

Acknowledgments

OpenAI - GPT-OSS-20B base model
Unsloth - Fast fine-tuning framework
Hugging Face - TRL, PEFT, Transformers
llama.cpp - GGUF conversion tools

Citation

If you use this model, please cite:

bibtex

@misc{hussain2026gptoss-stem,
  author = {Hussain, Khadim},
  title = {GPT-OSS-20B STEM Reasoning: Fine-tuned for Science Q&A with Chain-of-Thought},
  year = {2026},
  publisher = {Hugging Face},
  url = {https://huggingface.co/khadim-hussain/gpt-oss-20b-stem-reasoning-merged}
}

Also cite the original GPT-OSS model:

bibtex

@misc{openai2025gptoss,
  author = {OpenAI},
  title = {GPT-OSS: Open-Weight Language Models},
  year = {2025},
  url = {https://github.com/openai/gpt-oss}
}

License

Apache 2.0 (inherited from GPT-OSS)