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An audit of test-time search in world action models found the candidate selector barely beats random

AspireAI community · arXiv (cs.AI)
Test-time scaling in world action models is usually reported as a success rate, which hides whether the extra inference compute bought anything. This pre-registered audit on Cosmos Policy and RoboCasa checks all three links in the chain. On clean data a learned value selector is 1.66 percentage points worse than random, and a hindsight oracle gains only 1.40 points with an episode-level interval spanning zero; 82 percent of states show identical candidate outcomes, so there is little selection headroom to begin with. Token pruning cuts per-forward FLOPs by up to 47 percent but converts into at most a measured 1.15x end-to-end speedup on the deployed path, short of the authors' 1.5x target, and the adaptive-allocation experiment is inconclusive under a power gate. The authors also found and fixed a silent rendering corruption that worsens along compute-heavy planning paths while leaving the official direct-policy result untouched, and release a detector, fix and scripts.
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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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