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ThinkJev let a model think only where a statistical test proved it necessary, answering 24.5 percent of 8,359 decisions directly at a 3.9 percent realized error rate

AspireAI community · arXiv
Many production uses of a language model end in a typed decision - a pick from a closed option set whose probabilities code can act on - and reading those probabilities from one forward pass is fast but often wrong on multi-step questions such as arithmetic or date comparison. ThinkJev builds a fast and a slow system from one hybrid-thinking model: System 1 reads option probabilities from the direct answer, System 2 reads the same letters after the model has thought on the cached prompt, so escalating repeats no work. Without training, a statistical test on labeled dev data decides where System 1 may answer alone; at a 5% target, Qwen3.5-27B answered 24.5% of 8,359 test decisions that way with a realized error of 3.9%. The rest stopped each thought as soon as the answer was confident, reaching 81.6% accuracy against 82.7% for always thinking while using 72% of the thought tokens. The authors' own caveat is that choosing when to think from confidence alone saves less, because the decisions System 1 is least sure of are often not the ones thinking fixes.
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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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