Claude Reviewing Claude's Code

Anthropic's team has revolutionized their development process by having AI write and review its own code, creating a self-improving system that dramatically accelerates productivity while shifting human focus to higher-level concerns.

At Anthropic, the Claude Code team has become "patient zero" for a radically new development workflow where approximately 95% of their code is written by Claude itself. This team, which builds Claude Code (their AI coding product) using Claude Code, has created a virtuous cycle of self-improvement that's transforming how software gets built.

The process works like this: Claude generates pull requests (often larger than humans would typically review line-by-line), and then another instance of Claude reviews that code. Human engineers focus primarily on acceptance testing rather than detailed code review. This approach has proven so effective that it's spread beyond the core team - even engineers without TypeScript experience can now contribute to the TypeScript codebase by simply describing what they want to Claude and having it generate a pull request within an hour.

This shift has created unexpected bottlenecks in their development pipeline. Their merge queue had to be completely rearchitected because so much more code was being written and so many more pull requests were being submitted. Over 70% of Anthropic's pull requests are now Claude-generated, which completely overwhelmed their previous systems.

The key insight is that this approach doesn't eliminate the need for human involvement but shifts it to different areas. While code generation and basic review are increasingly handled by AI, humans focus on ensuring coherent product direction, packaging features for launch, and communicating with users. As Mike Krieger notes, "the classic things of building something useful for people and then making it known that you've built it and then learning from their feedback still exists - we've just made a portion of that whole process much more efficient."

This represents a fundamental shift in development practices that other companies will likely follow. The bottlenecks in software development are moving from code writing to the beginning of the process (deciding what to build) and the end (integrating and shipping). Teams that embrace this approach can dramatically accelerate their development velocity while freeing human creativity for the parts of the process where it adds the most value.