Boris Cherny: Building Claude Code
In a Nutshell
Boris Cherny explains how Opus 5 enables long-running autonomous agents and massive test-time compute through dynamic workflows that orchestrate thousands of agents across sequential and parallel stages. The key insight is that current models possess far more capability than products expose—unhobbling requires giving models harder tasks with verification tools rather than over-specifying instructions, and deleting accumulated constraints every 6 months. Self-maintaining codebases are now possible through 20-30 daily routines that handle dead code cleanup, experiment removal, test generation, and abstraction unification across all codebases.
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Boris Cherny, creator of Claude Code, joined for a discussion fresh off the Opus 5 release. The model achieved 30% on Arc AGI 3, representing a significant jump from previous low single digits or low teens scores.
Opus 5 demonstrates several novel capabilities compared to previous versions. The model can run for extended periods - days, weeks, or months at a time - particularly when combined with auto mode, without requiring scaffolding like SLGO. It also shows resistance to prompt injection, a capability that has been developing since Opus 4.7-4.8, with Sonnet 5 also performing well in this area.
The prompt injection resistance comes from three layers of protection: a well-aligned model representing three years of alignment research, a prompt injection classifier based on Chrisola's mechanistic interpretability work that monitors neurons in the model's brain for injection patterns, and an auto mode classifier. These three layers combined make prompt injection demonstrations impossible.
Over 80% of the system prompt was deleted from Claude Code with the Opus 5 release. This reflects the ongoing evolution of Claude Code as a product, where new models require deletion and modification of system prompts, tools, and tool prompts since behaviors that needed correction in previous models are now innate in newer versions.
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