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JevAgentHarness: Benchmarking, Deploying and Training Decision Models That Share Control with LLMs

Kunlun Zhu, Tao Feng, Xu Han, Heng Wang, Ling Yang, Xiangru Tang et al.

arXiv 2610.21412 44 pages Read the paper

The short version

The problem
Agents that use large language models for long tasks can be slow and costly because the large model makes nearly every small choice. A fast, smaller model may make mistakes, and one bad choice can change what the agent faces next.
The idea
The paper develops a way to test fast choice-making models both on sample questions and while they operate an agent, where their actions affect later steps. Its harness lets the fast model handle a choice only when its confidence passes a threshold learned from that agent’s own runs; otherwise, it asks the large model. The authors also train a compact model on the situations agents actually encounter, including situations following an error.
What it got
On unfamiliar tasks, agents using the trained compact model solved 91.5% of tasks, compared with 82.0% using JEV. On familiar task types, trained compact models cut costs by 81.1–89.0% and made agents up to 2.5 times faster without losing 3 or more percentage points of task success.

Modules from this paper

Confidence-Thresholded Delegation

Harness choices can save an LLM call but a wrong choice can derail later steps; JevAgentHarness turns choices into typed questions and delegates only when a per-choice confidence threshold fitted on agent trajectories is met.

agentsdecision-modelsconfidenceharnesses

Training Decision Models on Agent-Visited States

Fixed question sets miss the states an agent reaches after its own choices, so AgentDecision-4B trains on visited states—including states after mistakes—to better fit live control.

agentsdecision-modelstrainingSFT