Chess-SFT-6k — Global Chess Challenge 2025

Model Summary

Chess-SFT-6k is a small, text-only chess-playing language model fine-tuned via Supervised Fine-Tuning (SFT) to select legal and reasonable chess moves from symbolic board representations.
The model is designed for participation in the Global Chess Challenge 2025, where models must choose a legal move from a provided list without access to search, tools, or external engines at inference time.

This checkpoint represents an early-stopped SFT baseline, optimized to reduce illegal moves and catastrophic blunders, and intended as a foundation for reinforcement learning with verifiable rewards (GRPO).

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Model Details

• Developed by: Ritwika Kancharla
• Model type: Decoder-only causal language model
• Base model: Qwen/Qwen3-0.6B
• Language: English
• License: MIT
• Finetuned from: Qwen/Qwen3-0.6B
• Competition: Global Chess Challenge 2025 (AIcrowd × AGI House)

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Intended Use

Direct Use

• Selecting a single legal chess move (UCI format) from:
  • FEN position
  • Side to move
  • List of legal moves
• Text-only inference without any tools, engines, or search
• Compatible with the Global Chess Challenge starter kit and evaluation pipeline

Downstream Use

• Research on reasoning and decision-making in small language models
• Experiments with curriculum learning and reinforcement learning (GRPO / RLVR)
• Educational or analytical chess assistants (non-engine-based)

Out-of-Scope Use

• Replacement for classical chess engines
• Deep tactical calculation or forced-mate search
• Real-money, rated, or professional chess play
• Any inference-time use of Stockfish, search, or external tools

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Training Details

Training Data

• Dataset: aicrowd/ChessExplained
• Dataset file: ChessExplained_2500k_qwen3.parquet
• Dataset size: ~2.5M positions (~1.04 GB)
• Content:
  • Symbolic chess positions
  • Legal move lists
  • Natural language explanations
• Stockfish was used only offline for data generation and evaluation.
• No external tools or engines are used at inference time.

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Training Procedure

• Method: Supervised Fine-Tuning (SFT)
• Objective: Next-token prediction (Negative Log-Likelihood)
• Precision: bf16 mixed precision
• Optimizer: AdamW
• Epochs: 1
• Total steps: ~10,100
• Checkpoint selection: Early stopping based on evaluation metrics

Training Loss Progression (Selected)

Although training loss continued to decrease after 6k steps, chess performance began to regress, motivating early stopping.

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Evaluation

Evaluation Setup

• Evaluation performed using the official Global Chess Challenge baseline
• Legal move enforcement handled by the environment
• Move quality evaluated using Stockfish (depth 20)
• Metrics computed over full games

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Metrics

• Average Centipawn Loss (ACPL)
• Win / draw / loss rates
• Illegal move rate
• Puzzle success rate

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Results Across Checkpoints

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Evaluation Summary

• Early training significantly reduced illegal moves and catastrophic blunders.
• ACPL vs Stockfish improved sharply up to ~6,000 steps.
• Continued SFT beyond this point led to regression despite lower training loss.
• Checkpoint 6,000 provided the best trade-off between stability and chess strength.

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Bias, Risks, and Limitations

• The model does not perform search and may miss deep tactical combinations.
• Performance depends on patterns learned from supervised data.
• Natural language explanations are not guaranteed to reflect optimal chess reasoning.
• Like all chess-playing LLMs, the model may struggle in rare or highly tactical positions.

Recommendations

This model should be treated as a research artifact rather than a competitive chess engine.
Best performance is expected when combined with curriculum learning and reinforcement learning fine-tuning.

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Technical Specifications

Architecture

• Decoder-only Transformer
• Autoregressive next-token prediction
• Chat template and tokenizer inherited from Qwen3

Compute Infrastructure

• Training hardware: NVIDIA H100 (Kaggle)
• Evaluation: CPU/GPU
• Frameworks: PyTorch, Hugging Face Transformers, vLLM
• Chess environment: python-chess (evaluation only)

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Environmental Impact

• Cloud provider: Kaggle
• Hardware: NVIDIA H100
• Training duration: A few hours
• Carbon emissions: Not formally estimated

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Code and Reproducibility

• Training & evaluation codebase:
  https://github.com/AIcrowd/Global-Chess-Challenge-2025-Baselines
• Key scripts:
  • train.py
  • run_evaluation.py

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Citation

If you use this model, please cite the base model and the competition:

Base model:
Qwen/Qwen3-0.6B

Competition:
Global Chess Challenge 2025 (AIcrowd & AGI House)

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Model Card Authors

Ritwika Kancharla

Contact

Via Hugging Face profile