We Cut 80% of Claude Code's Prompt: Boris Cherny on Radical Simplicity
Why deleting 80% of Claude Code's system prompt made the model smarter, told through creator Boris Cherny's context engineering and the discipline of subtraction — a WOW Mentor teardown.
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We Cut 80% of Claude Code's Prompt: Boris Cherny on Radical Simplicity
Narration: WOW Mentor
WOW Mentor breaks down the strategy of Boris Cherny, the creator of Claude Code who, timed to the release of Opus 5, deleted more than 80 percent of the tool's system prompt and made the model smarter in the process. Each time a new model lands, he argues, you should delete your prompts and code and use ablation to add them back one line at a time, treating the model like a living creature and handing it a slightly-too-hard task alongside a way to verify its own work. From a model that no longer falls for prompt injection, to a language rewrite finished in eleven days, to a task still running by itself after two weeks, to thousands of agents that maintain the codebase on their own — the through-line is always the courage to delete and the discipline of the empirical.
- When a new model ships, delete your system prompt, CLAUDE.md, skills, and hooks first. Most of the rules you stacked up for older models are dead weight now, and deleting them often makes the model smarter.
- Don't refill deleted rules by guessing. Run the product for real, and add a line back only when the model stumbles over the same thing repeatedly. Ablation is an eval where you delete things to measure each line's impact.