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Introduction

NEW IN 2026 

Harness engineering emerged through 2026 as a distinct discipline, formalized in surveys covering 100+ papers and 23 production systems. The core claim: at fixed model capability, agent-computer interface design materially changes benchmark outcomes.

The Equation:

 Agent = Model + Harness

The harness treats the LLM as a frozen reasoning utility and moves the responsibility for safety, execution accuracy, multi-step orchestration, and adaptive memory into the surrounding infrastructure. A production harness is generally described as a three-layer system:

Layer

Responsibility

Information Layer

What data the agent can observe; what tools it may invoke at a given moment; vector storage, memory compilation, tool registries.

Control Layer

Planner / generator / evaluator roles; structured handoff artefacts; verification gates; state machines governing step sequencing.

Governance Layer

Permission boundaries, policy checks, approval gates, and the audit trail that makes autonomy observable.