Harness Engineering in 2026: From Prompt Tricks to Programmable Control Plans Harness engineering is no longer a buzzword; it is the new discipline underpinning reliable, large‑scale AI systems. After a brief flirtation with prompt engineering (“what magical incantation unlocks the model?”) and context engineering (“how do I fill the context window?”), practitioners have realized the real work happens in the control plane that wraps around a model. That plane is the harness . This article synthesises recent research, industry case studies and design patterns to show what harness engineering really means, why multi‑agent orchestration is hard, and how to build safe systems in regulated domains like mortgages, operations and various areas. Along the way we address common criticisms—shallow definitions, hand‑wavy case studies, weak security coverage—and fill gaps on token economics, state consistency and evaluation methodologies. A Clear Definition Harness engineering is the...