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Sanity Checks for Sparse Autoencoders: Do SAEs Beat Random Baselines? (arxiv.org)
2 points by yorwba 221 days ago | hide | past | pdf | discuss on HN

In plain words: Sparse autoencoders split a neural network's internal signals into a few supposedly meaningful pieces. Tested on data with known pieces, they recovered only 9% even while rebuilding the signals well, and versions with random pieces scored about the same as fully trained ones.

Abstract

Sparse Autoencoders (SAEs) have emerged as a promising tool for interpreting neural networks by decomposing their activations into sparse sets of human-interpretable features. Recent work has introduced multiple SAE variants and successfully scaled them to frontier models. Despite much excitement, a growing number of negative results in downstream tasks casts doubt on whether SAEs recover meaningful features. To directly investigate this, we perform two complementary evaluations. On a synthetic setup with known ground-truth features, we demonstrate that SAEs recover only $9\%$ of true features despite achieving $71\%$ explained variance, showing that they fail at their core task even when reconstruction is strong. To evaluate SAEs on real activations, we introduce three baselines that constrain SAE feature directions or their activation patterns to random values. Through extensive experiments across multiple SAE architectures, we show that our baselines match fully-trained SAEs in interpretability (0.87 vs 0.90), sparse probing (0.69 vs 0.72), and causal editing (0.73 vs 0.72). Together, these results suggest that SAEs in their current state do not reliably decompose models' internal mechanisms.

Anton Korznikov, Andrey Galichin, Alexey Dontsov, Oleg Rogov, Ivan Oseledets, Elena Tutubalina
arXiv:2602.14111 · cs.LG · submitted Feb 15, 2026
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