@inproceedings{
jenner2024evidence,
title={Evidence of Learned Look-Ahead in a Chess-Playing Neural Network},
author={Erik Jenner and Shreyas Kapur and Vasil Georgiev and Cameron Allen and Scott Emmons and Stuart Russell},
booktitle={The Thirty-eighth Annual Conference on Neural Information Processing Systems},
year={2024},
url={https://openreview.net/forum?id=8zg9sO4ttV}
}
Do neural networks learn to implement algorithms such as look-ahead or search "in the wild"? Or do they rely purely on collections of simple heuristics? We present evidence of *learned look-ahead* in the policy and value network of Leela Chess Zero, the currently strongest deep neural chess engine. We find that Leela internally represents future optimal moves and that these representations are crucial for its final output in certain board states. Concretely, we exploit the fact that Leela is a transformer that treats every chessboard square like a token in language models, and give three lines of evidence: (1) activations on certain squares of future moves are unusually important causally; (2) we find attention heads that move important information "forward and backward in time," e.g., from squares of future moves to squares of earlier ones; and (3) we train a simple probe that can predict the optimal move 2 turns ahead with 92% accuracy (in board states where Leela finds a single best line). These findings are clear evidence of learned look-ahead in neural networks and might be a step towards a better understanding of their capabilities.
Evidence of Learned Look-Ahead in a Chess-Playing Neural Network
Erik Jenner Shreyas Kapur Vasil Georgiev Cameron Allen Scott Emmons Stuart Russell