Cherny: Only Add System Prompt Instructions When Models Repeatedly Stumble
Boris Cherny · Boris Cherny: We Cut 80% of Claude Code’s Prompt · Y Combinator · Jul 27, 2026 · at 7:55
Boris Cherny, Head of Claude Code at Anthropic, outlines the empirical methodology for rebuilding system prompts from scratch on new model releases.
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“The thing that you want to do is you want to run it. And if it's like a custom agentic product that you're building, you want to kind of run the products. You want to see where it fails with the model. You want to see what it does well. If you're using quad code, you want to see where it does well with your code base, or maybe where it stumbles over, you know, the architecture or stumbles over something else. And only when you see it repeatedly stumble on the same thing, That's when you add it back.”
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