Mixing 8% flawed reasoning traces lifts a chess LLM to 1300 Elo
amasad · x · 2026-07-29
A chess LLM training experiment found that pure board→move supervision hit strong diminishing returns. An accidental branch that tried to “think before you move” produced hallucinated moves, but mixing just about 8% of those reasoning traces into the training mix beat pure move data at the same compute budget.
- The model reached 1300 Elo.
- Pure board→move pairs plateaued quickly.
- A small slice of flawed reasoning traces helped the model internalize the thinking process without needing to execute it at inference time.
Related event: LLMs Still Struggle with Chess Despite Pre-training(3 posts)→
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