Prompt-injection defenses and WebFetch

Boris details three-layer defenses: model alignment, runtime classifiers, and summarizing web content via subagents.

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Boris Cherny is the creator and Head of Claude Code at Anthropic. He previously spent five years at Meta as a Principal Engineer and is the author of the book Programming TypeScript.

In this episode of Pragmatic Engineer, we went through how Claude Code was built and what it means when engineers no longer write most of the code themselves.

We discuss how Claude Code evolved from a side project into a core internal tool at Anthropic and how Boris uses it day-to-day. We go deep into workflow details, including parallel agents, PR structure, deterministic review patterns, and how the system retrieves context from large codebases. We also get into how Claude Cowork was built.

As coding becomes more accessible, the role of engineers shifts rather than shrinks. We examine what that shift means in practice, which skills become more important, and why the lines between product, engineering, and design are blurring.

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Timestamps

(00:00) Intro

(11:15) Lessons from Meta

(19:46) Joining Anthropic

(23:08) The origins of Claude Code

(32:55) Boris's Claude Code workflow

(36:27) Parallel agents

(40:25) Code reviews

(47:18) Claude Code's architecture

(52:38) Permissions and sandboxing

(55:05) Engineering culture at Anthropic