arXiv AI By Chenglin Yang

Evaluate the Stack, Not the Layer: Do Deterministic and LLM Gates for Agent Actions Fail Independently?

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The study evaluates how runtime gates for agent tool calls stack, assuming their errors multiply. Using 1,119 labeled agent actions from three corpora, the authors compare a deterministic rule layer with four LLM judges, measuring the effective number of multiplication-equivalent layers (n_mult). Results show that two judges compose to about 1.2–1.4 layers, while a rule layer plus one judge composes to roughly 1.86–2.09 layers, with variations depending on miss definitions and corpora.

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arXiv AI
Sep 2

Commit-first LLM judging inherits the judge's own errors

The paper investigates whether widely used evaluation frameworks for large language models (LLMs) implement a defense called commit‑first judging, which requires a judge to solve a task itself before accepting a candidate answer. Across 24 configurations in eight popular frameworks, none use the full commit‑first method; nine use a weaker variant that is ineffective. In controlled experiments, the weaker variant allowed systems to game the judge, while the full commit‑first approach eliminated this vulnerability but sometimes worsened evaluation when the judge’s own answer was incorrect.

By Idil Gozel
arXiv AI
Sep 2

trajectory-judge: What Outcome-Only LLM Judges Miss on Agent Trajectories

The paper "trajectory-judge: What Outcome-Only LLM Judges Miss on Agent Trajectories" examines the limitations of outcome-only evaluation for large language model agents. Using a deterministic tool‑using support‑desk environment with a scripted oracle policy and a fault injector, the authors compare five different judging approaches—programmatic rules, outcome‑only, step‑rubric at two model sizes, and a self‑consistency ensemble—on metrics such as detection, step localisation, fault typing, calibration, and cost across 400 trajectories. The study finds that outcome‑only judges miss many silent faults and generate false positives, while step‑rubric judges achieve higher recall with no false alarms but at greater cost, and that none of the judges read the final reply, allowing fabricated promises to evade detection. "whyItMatters":"The findings highlight that current production‑default outcome‑only evaluations can overlook critical failures in agent behavior, underscoring the need for more nuanced, step‑level judging methods to ensure reliable LLM agent performance."

By Hadi Mohammadi