The paper 'AI4AI at Test-Time: Strong-to-Weak Capability Transfer via Harnesses' from Salesforce AI and UIUC sets up a core scenario: a stronger Builder AI observes the errors of a weaker Target AI in an open programming environment and designs a harness for it—an external working mechanism including task classification, prompt selection, Python programs, state rules, and answer checking. The Builder only sees a random 5% of the validation set for each benchmark, and the final harness is frozen and used on the unseen hidden test set.
In the main experiment, GPT-5.4-mini's average accuracy when run bare is 0.488, rising to 0.763 on average with the automatically constructed harness, and 0.912 at best, a relative improvement of about 86.7%. For comparison, the stronger GPT-5.4 achieves only 0.619 when run bare. All 57 scaffold runs for GPT-5.4-mini exceeded the original baseline, and all 11 Builder configurations produced positive average improvements.
The paper also compares a human-designed UserHarness: GPT-5.4-mini + Human-Inspired Harness reaches 0.939, while the best automatic harness at 0.912 is close, but still lags on complex benchmarks.