JIT-Agent: Scaling Harness Intelligence via Just-in-Time Harness Evolution
TL;DR - JIT-Agent is a model that generates and repairs task-specific agent harnesses at runtime, adapting memory, planning, action protocols, and tool orchestration for off-the-shelf LLMs. The results suggest harness optimization can improve agent performance independently of—and sometimes more than—switching to a stronger foundation model.
- Formalizes agent harnesses as machine-generatable artifacts built from a fixed four-module protocol.
- Learns to customize harnesses per task, repair them for reliable execution, and evolve them using archived performance signals.
- With generated harnesses, DeepSeek-V4-Flash reportedly exceeds GPT-5.6 by 9.1 points on DeepSearchQA and 4.3 on OdysseyBench; GLM-5.2 gains up to 20.2 points.
- Generated harnesses are competitive with mature runtimes such as OpenCode and Claude Code and consistently improve several model families.