Tracing the Thought of a Grandmaster-level Chess-Playing Transformer

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Hauptverfasser: Lin, Rui, Jin, Zhenyu, Zhou, Guancheng, Ge, Xuyang, Shu, Wentao, Wu, Jiaxing, Wang, Junxuan, He, Zhengfu, Zhang, Junping, Qiu, Xipeng
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Veröffentlicht: 2026
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author Lin, Rui
Jin, Zhenyu
Zhou, Guancheng
Ge, Xuyang
Shu, Wentao
Wu, Jiaxing
Wang, Junxuan
He, Zhengfu
Zhang, Junping
Qiu, Xipeng
author_facet Lin, Rui
Jin, Zhenyu
Zhou, Guancheng
Ge, Xuyang
Shu, Wentao
Wu, Jiaxing
Wang, Junxuan
He, Zhengfu
Zhang, Junping
Qiu, Xipeng
contents While modern transformer neural networks achieve grandmaster-level performance in chess and other reasoning tasks, their internal computation process remains largely opaque. Focusing on Leela Chess Zero (LC0), we introduce a sparse decomposition framework to interpret its internal computation by decomposing its MLP and attention modules with sparse replacement layers, which capture the primary computation process of LC0. We conduct a detailed case study showing that these pathways expose rich, interpretable tactical considerations that are empirically verifiable. We further introduce three quantitative metrics and show that LC0 exhibits parallel reasoning behavior consistent with the inductive bias of its policy head architecture. To the best of our knowledge, this is the first work to decompose the internal computation of a transformer on both MLP and attention modules for interpretability. Combining sparse replacement layers and causal interventions in LC0 provides a comprehensive understanding of advanced tactical reasoning, offering critical insights into the underlying mechanisms of superhuman systems. Our code is available at https://github.com/JacklE0niden/Leela-SAEs.
format Preprint
id arxiv_https___arxiv_org_abs_2604_10158
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Tracing the Thought of a Grandmaster-level Chess-Playing Transformer
Lin, Rui
Jin, Zhenyu
Zhou, Guancheng
Ge, Xuyang
Shu, Wentao
Wu, Jiaxing
Wang, Junxuan
He, Zhengfu
Zhang, Junping
Qiu, Xipeng
Machine Learning
While modern transformer neural networks achieve grandmaster-level performance in chess and other reasoning tasks, their internal computation process remains largely opaque. Focusing on Leela Chess Zero (LC0), we introduce a sparse decomposition framework to interpret its internal computation by decomposing its MLP and attention modules with sparse replacement layers, which capture the primary computation process of LC0. We conduct a detailed case study showing that these pathways expose rich, interpretable tactical considerations that are empirically verifiable. We further introduce three quantitative metrics and show that LC0 exhibits parallel reasoning behavior consistent with the inductive bias of its policy head architecture. To the best of our knowledge, this is the first work to decompose the internal computation of a transformer on both MLP and attention modules for interpretability. Combining sparse replacement layers and causal interventions in LC0 provides a comprehensive understanding of advanced tactical reasoning, offering critical insights into the underlying mechanisms of superhuman systems. Our code is available at https://github.com/JacklE0niden/Leela-SAEs.
title Tracing the Thought of a Grandmaster-level Chess-Playing Transformer
topic Machine Learning
url https://arxiv.org/abs/2604.10158