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Any token-level RL advantage splits into two stages, and GRPO estimators that handle only one of them leak credit

AspireAI community · arXiv (cs.AI)
This paper factors any token-level advantage in Group Relative Policy Optimization into sample-level baselining and token-level credit assignment, then shows that affine baselines let heavy-tailed and binary reward shapes propagate into the gradient while unnormalized token credit rules fail to conserve the total credit a verifier issued. TACE replaces linear standardization with a one-dimensional optimal-transport map to a standard normal, then rank-calibrates token weights so their mass and sign are conserved, with proofs for inter-task moment equity, a deterministic tail bound and mass conservation. On a multimodal reasoning suite it posts the strongest results on a majority of benchmarks but does not dominate every setting. The limitation is stated by the authors themselves: the advantage is not uniform across all benchmarks.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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.
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