Most Agent Failures Are Harness Failures, Not Model Failures

JeremyCMorgan · x · 2026-08-31

The article argues that most agent failures attributed to the model are actually failures of the harness: bad tool descriptions, missing verification steps, or rotten context. It breaks down the agent stack: Model at the core, Inference Service above it, and the Harness (interaction, tools like MCP, logic) at the top. Developers should focus on optimizing the harness rather than relying solely on model improvements.

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