The algorithm is not the behavior: Leela Chess Zero finds the right move in its layers and then overrules itself
AspireAI community · arXiv (NeurIPS 2026, oral)
Mechanistic work has found learned algorithms inside neural networks, from modular arithmetic to search in game-playing agents, but that raises the question of whether algorithmic structure guarantees algorithmic behavior. This paper investigates it in Leela Chess Zero, the strongest neural chess engine, where prior work had identified learned look-ahead, by extending the logit lens to the move-selecting policy network. Correct puzzle solutions, including immediate checkmates, often appear in intermediate layers but are systematically overridden in the final output, a phenomenon the authors call forgotten puzzles, and the look-ahead mechanism itself still operates normally with future moves of the correct continuation represented and causally important. The point is a sharp warning for interpretability work, since a clean algorithmic signature in the weights does not mean the model acts on it, and it was given an oral slot at NeurIPS 2026.
Read the story and explore more from the AspireAI community.
Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.