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Structural Instability of Feature Composition

Summary

Sparse Autoencoders (SAEs) effectively disentangle feature superposition in transformers, but compositional steering suffers from geometric instability. This paper introduces a high-dimensional cone manifold framework, derives an asymptotic collapse threshold, and shows that ReLU rectification causes a ratchet-like interference accumulation. Experiments on CLEVR validate the predictions.

SourcearXiv Machine LearningAuthor: Yunpeng Zhou
Structural Instability of Feature Composition
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[2605.05223] Structural Instability of Feature Composition

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Computer Science > Machine Learning

arXiv:2605.05223 (cs)

[Submitted on 18 Apr 2026]

Title:Structural Instability of Feature Composition

Authors:Yunpeng Zhou

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Abstract:Sparse Autoencoders (SAEs) have emerged as a powerful paradigm for disentangling feature superposition in transformer-based architectures, enabling precise control via activation steering. However, the theoretical foundations of compositional steering -- the simultaneous activation of distinct semantic latents -- remain under-explored. The prevailing Linear Representation Hypothesis often abstracts away non-linear interference effects that arise in overcomplete dictionaries. We present a geometric framework for analyzing the instability of feature unions. Modeling the activation space as a high-dimensional sparse cone manifold, we derive an asymptotic compositional-collapse threshold under a spherical dictionary model, characterized by the Gaussian mean width (statistical dimension) of the signal cone. We further show that, in the high-bias regime, ReLU rectification converts microscopic correlation-induced variance fluctuations into a systematic drift that accumulates under composition, yielding interference growth consistent with a ratchet effect. We validate the predicted scaling trends on structured semantic features extracted from CLEVR, where hierarchical correlations accelerate the transition relative to random baselines. Together, our results highlight geometric constraints on the scalability of union-based steering and motivate composition mechanisms that explicitly manage interference beyond naive linear superposition.

Subjects:

Machine Learning (cs.LG); Artificial Intelligence (cs.AI)

Cite as: arXiv:2605.05223 [cs.LG]

(or arXiv:2605.05223v1 [cs.LG] for this version)

https://doi.org/10.48550/arXiv.2605.05223

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arXiv-issued DOI via DataCite

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From: Yunpeng Zhou [view email] [v1] Sat, 18 Apr 2026 05:53:31 UTC (49 KB)

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Key points and analysis

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Key points

  • SAEs can disentangle feature superposition but compositional steering is theoretically unstable.
  • A geometric framework derives an asymptotic collapse threshold characterized by the Gaussian mean width of the signal cone.
  • In the high-bias regime, ReLU rectification converts microscopic fluctuations into systematic drift, producing ratchet-effect interference.
  • Predictions are validated on CLEVR, where hierarchical correlations accelerate the collapse transition.

Highlights and analysis are generated automatically and may contain errors. Check the original source.