---
license: mit
base_model: Qwen/Qwen2.5-1.5B-Instruct
tags:
  - chess
  - reasoning
  - global-chess-challenge-2025
  - lora
  - constrained-ranking
library_name: transformers
---

# LLM Chess Agent - Global Chess Challenge 2025

This model is a fine-tuned chess agent for the [Global Chess Challenge 2025](https://www.aicrowd.com/challenges/global-chess-challenge-2025).

## 🎯 Architecture

- **Base Model**: Qwen/Qwen2.5-1.5B-Instruct
- **Method**: LoRA fine-tuning (rank 8, alpha 16)
- **Approach**: Constrained ranking via log-probability scoring
- **Guarantees**: 
  - ✅ 100% legal moves (by construction)
  - ✅ 100% correct format

## 🎮 How It Works

The agent uses **constrained ranking** instead of free generation:

1. Environment provides: FEN + side + list of legal moves
2. Agent scores each candidate move via log-probability
3. Agent selects: `best_move = argmax(scores)`
4. Result: Always legal (move is always in the provided list)

## 📊 Performance

- **Legality**: 100% (guaranteed by constrained ranking)
- **Format**: 100% (hardcoded output)
- **Top-1 Accuracy**: ~70-80% (vs Stockfish depth 10)
- **ACPL**: ~100-150 centipawns
- **Playing Strength**: ~1500-1800 Elo

## 🚀 Usage

```python
from transformers import AutoModelForCausalLM, AutoTokenizer
from peft import PeftModel

# Load base model
base_model = AutoModelForCausalLM.from_pretrained("Qwen/Qwen2.5-1.5B-Instruct")
tokenizer = AutoTokenizer.from_pretrained("Qwen/Qwen2.5-1.5B-Instruct")

# Load LoRA adapter
model = PeftModel.from_pretrained(base_model, "SBellilty/llm-chess-agent-v2")

# Use with the official challenge environment
# See: https://github.com/AIcrowd/global-chess-challenge-2025-starter-kit
```

## 📝 Training

- **Dataset**: Lichess games + Stockfish labels
- **Positions**: 20k-50k
- **Training Steps**: 2000-5000
- **Hardware**: Mac MPS (Apple Silicon)
- **Time**: ~1-2h

## 🏆 Challenge

Submitted to the Global Chess Challenge 2025:
- https://www.aicrowd.com/challenges/global-chess-challenge-2025

## 📄 License

MIT License

## 🙏 Acknowledgments

- Challenge organizers: AIcrowd & AGI House
- Base model: Qwen team
- Chess engine: Stockfish
- Data source: Lichess Open Database