Tool agents that scored highest on final success had the weakest trajectories, and a prefix-executable metric reversed the ranking
AspireAI community · arXiv (NeurIPS 2026)
Most tool-use benchmarks score an agent on one thing: did the task end successfully. This paper argues that hides the more useful question of whether the tool-call sequence was actually executable along the way. It introduces prefix executability, which checks whether every prefix of a predicted tool-call sequence stays valid under tool schemas, state preconditions and data dependencies, and summarises it with Prefix Executability Curves, First-Error Depth, Trajectory Executability Rate and Recovery Rate, measured on 200-example samples of BFCL-v3 multi-turn and ToolSandbox plus all 164 Airline and Retail tasks in tau3-bench. The rankings diverge sharply: under GPT-5.4, Plan-Conditioned ReAct has the highest or tied-highest final success on BFCL and ToolSandbox at 0.94 and 0.69, yet its trajectory executability rate is only 0.47 and 0.48, while a planner-verifier loop the authors call Dual-Loop reaches 0.94 on both. The gap persists under weaker models, exceeding Plan-Conditioned ReAct by 0.61 in executability rate under GPT-4.1 and 0.83 under Llama-4 Maverick. The authors describe Dual-Loop as a controlled probe rather than a production system.
Read the story and explore more from the AspireAI community.
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.