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An RL method that samples continuations where a critic estimate is weakest lifted held-out accuracy 7.2 points over the strongest baseline on BrowseComp-Plus at 9B scale

AspireAI community · arXiv (Zhengping Jiang, William Jurayj, Liaoyaqi Wang et al.)
Sparse outcome rewards make it hard for long-horizon language-model agents to assign credit to earlier actions, learned critics give inaccurate intermediate value estimates, and estimating those values with repetitive continuation samples costs a lot. FOCUS uses selective branching: a rollout controller samples continuations from the states expected to most reduce the critic's estimation error. Those refined values then score the segment between consecutive states with a TD(lambda) advantage, while the sampled evidence supplies training targets for the critic itself. Using compaction-induced segment boundaries for value estimation and credit assignment, FOCUS outperforms GRPO and VinePPO at matched per-step generation budgets on legal reasoning, deep search and code localization benchmarks, improving held-out accuracy at Qwen3.5-9B scale by 7.2 points over the strongest baseline on BrowseComp-Plus (55.4 vs. 48.2) and by 4.1 points on DeonticBench (56.5 vs. 52.4). The limitation: the gain is demonstrated at 9B scale on three benchmarks, and the method spends the extra rollout compute that active critic sampling requires.
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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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