Learn to build custom harnesses, folks! Here is an impressive paper showing the impact of a good custom harness on long-context work. GLM-5.3-Flash goes from 4.4% to 61.1% exact match on OfficeQA Pro V2 with the same model. The authors report that the gain comes from the harness. The model-agnostic harness name is LongHarness, built for corpora of 100M tokens and more. Why it works: Standard agent harnesses keep evidence and conclusions mixed into one growing chat history. Retrieval keeps…