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A generative critic that writes reasons instead of scalars gave LLM agents a more stable off-policy training signal

AspireAI community · arXiv
Training LLM agents without expert demonstrations usually means policy gradients against a sparse reward, which gets noisy and sample-hungry over long horizons, especially when the action space is natural language. Natural Language Actor-Critic replaces the scalar-value critic with a generative LLM critic that produces natural-language critique, giving the policy a richer signal about why an action was suboptimal and reducing the need for random exploration. It also trains off-policy without policy gradients, which the authors argue is a more data-efficient and stable alternative to on-policy methods. Results on a mixture of reasoning, web browsing, tool-use and dialogue tasks show NLAC promising against existing training approaches. The limitation the paper itself states: the evidence is on a mixture of task types and the results are described as showing promise, so this is a direction rather than a settled win over PPO-style agent training.
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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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