UofTCSSLab/C1-4B

TEXT GENERATIONConcurrent Unit Cost:1Model Size:4BQuant:BF16Context Size:32kTool Calling:SupportedPublished:Jun 22, 2026License:apache-2.0Architecture:Transformer Open Weights Featherless Exclusive Cold

UofTCSSLab/C1-4B is a 4 billion parameter language model developed by UofTCSSLab, specifically fine-tuned for grounded chess reasoning. This model analyzes chess positions step-by-step in natural language and outputs the best move in UCI notation. It achieves 48.3% accuracy on a 900-puzzle test set, demonstrating its specialization in strategic chess analysis. The model is designed for applications requiring detailed, human-readable chess move explanations and optimal move suggestions.

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UofTCSSLab/C1-4B: Grounded Chess Reasoning Model

UofTCSSLab/C1-4B is a 4 billion parameter language model developed by UofTCSSLab, specifically engineered for advanced chess reasoning. This model excels at analyzing complex chess positions, providing step-by-step natural language explanations, and identifying the optimal move in UCI notation.

Key Capabilities

  • Grounded Chess Reasoning: Analyzes chess positions (provided in FEN, piece arrangements, and legal moves) and generates detailed reasoning.
  • Optimal Move Prediction: Concludes its analysis with a single best move in UCI format (e.g., e2e4).
  • Performance: Achieves a 48.3% accuracy on a 900-puzzle test set for exact-match UCI moves, outperforming its SFT-stage base model (42.3%).
  • Instruction-Tuned: The model is the final (SFT + RL) version, indicating refinement through supervised fine-tuning and reinforcement learning.

Recommended Usage

  • Greedy Decoding: It is strongly recommended to use greedy decoding (temperature 0) for optimal performance and consistent output.
  • Prompt Structure: Users should provide the FEN, piece positions, and legal moves, requesting a step-by-step analysis ending with FINAL_ANSWER: <uci_move>.

Good for

  • Chess Analysis Tools: Integrating AI for explaining chess moves and strategies.
  • Educational Platforms: Providing detailed insights into chess game progression.
  • Automated Chess Commentaries: Generating human-like commentary for chess matches.