New John Hopkins and Carnegie Mellon University Paper Shows that a small model can learn to improve an agent's harness code from run results, and the skill transfers to new tasks.

A small model trained to rewrite an agent's harness code from failure reports can adapt agents to new tasks, so let it tune your harness instead of doing it by hand.

The harness is the code that decides what the model sees and which tools it calls. The editor reads the harness and what failed, then writes a code change, rewarded by how well the new harness scores.

On 21 unseen reasoning task types, a 4B editor's average edit score rose from 0.32 to 0.62, above its 35B teacher. A separate editor trained on HotpotQA kept improving harnesses on 2 other QA benchmarks.

Run it for several rounds per task, since repeated edits beat single fixes.