Understanding Scaling Laws in Deep Neural Networks via Feature Learning Dynamics
- URL: http://arxiv.org/abs/2512.21075v1
- Date: Wed, 24 Dec 2025 09:39:04 GMT
- Title: Understanding Scaling Laws in Deep Neural Networks via Feature Learning Dynamics
- Authors: Zihan Yao, Ruoyu Wu, Tianxiang Gao,
- Abstract summary: We show that scaling laws describe what success looks like but not when and why scaling succeeds or fails.<n>A central obstacle is the lack of a rigorous understanding of feature learning at large depth.
- Score: 9.885471525709113
- License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
- Abstract: The empirical success of deep learning is often attributed to scaling laws that predict consistent gains as model, data, and compute grow; however, large models can exhibit training instability and diminishing returns, suggesting that scaling laws describe what success looks like but not when and why scaling succeeds or fails. A central obstacle is the lack of a rigorous understanding of feature learning at large depth. While muP characterizes feature-learning dynamics in the infinite-width limit and enables hyperparameter transfer across width, its depth extension (depth-muP) breaks down for residual blocks with more than one internal layer. We derive Neural Feature Dynamics (NFD) for ResNets with single-layer residual blocks, characterizing feature learning via a coupled forward-backward stochastic system in the joint infinite-width and infinite-depth limit. In this regime, NFD identifies when scaling-law trends persist and explains diminishing returns. It also reveals a vanishing mechanism induced by the 1/sqrt(depth) residual scaling under which the gradient-independence assumption (GIA), known to fail during training at finite depth, becomes provably valid again at infinite depth, yielding an analytically tractable regime for end-to-end feature learning. Motivated by this insight, we study two-layer residual blocks and show that the same mechanism causes feature-learning collapse in the first internal layer at large depth, providing a structural explanation for the empirical failure of depth-muP. Based on this diagnosis, we propose a depth-aware learning-rate correction that counteracts the collapse and empirically restores depth-wise hyperparameter transfer, yielding stronger performance in deeper ResNets.
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