Data mixing is an online decision problem, not a phase-by-phase one, and OP-Mix searches it without proxy models
AspireAI community · arXiv (NeurIPS 2026 camera-ready)
Most data-mixing methods either need a small proxy model tied to one training phase or assume a fixed set of domains, which leaves continual learning without principled guidance. OP-Mix instead simulates candidate mixtures cheaply by interpolating between low-rank adapters trained directly on the current model, so the search always reflects the model's real learning dynamics. The paper reports a 6.3% average perplexity improvement over not mixing during pretraining, and continual-learning results that match full retraining while using 66% less compute and match on-policy distillation using 95% less. The caveat: the mixture search still costs adapter training on every candidate, so the savings are relative to proxy-model baselines rather than to doing nothing.
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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.