๐Ÿ’ป Tom Tunguz: The AI Harness Now Matters More Than the Model

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๐Ÿ’ป Tom Tunguz: The AI Harness Now Matters More Than the Model

Tunguz argues the harness โ€” the scaffolding wrapped around a model โ€” has become the faster-moving variable in AI coding cost and quality.
โ€ข OpenAI's GPT-5.5 scored 61.5% functional correctness in its native Codex harness, but 87.2% in Cursor's harness โ€” a 25.7-point swing.
โ€ข Anthropic's Opus 4.7 also scored higher in a rival's harness (91.1% in Cursor) than its own (87.2% in Claude Code).
โ€ข The harness now "owns the prefix," accounting for 86-98% of the total bill.

๐Ÿ’ก Why it matters: If the harness drives more of the performance gap than the underlying model, buyers and builders may need to re-evaluate vendor lock-in and tooling choices as much as model selection โ€” a shift in where competitive advantage in AI coding actually sits.

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