Boris Cherny explains how Claude Code cut 80% of its system prompt
Y Combinator · youtube · 2026-07-28
Boris Cherny on how Claude Code was built
In this Startup School 2026 interview, Boris Cherny—creator of Claude Code—talks about what changed with Opus 5, how Claude Code evolved, and how fast underlying model capabilities are reshaping product design.
Key points covered in the talk:
- Claude Code’s approach to prompt injection and why the team deleted about 80% of its system prompt.
- How the product was rebuilt after learning to “press delete” on over-engineered prompts.
- The idea of product overhang and “unhobbling” AI as model capability keeps accelerating.
- Running thousands of AI agents and why coding is now “almost solved.”
- What CS students should still learn even as coding workflows change.
The session is framed as a practical look at building an AI coding product when the model underneath is improving faster than the product cycle.
Related event: Claude Code Creator Reveals Opus 5 Design Insights in YC Interview(4 posts)→
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