Anthropic says Claude now writes about 90% of Claude Code's own code and explains how it changed code review to keep up
Claude writes about 90% of Claude Code's code. From June to September, merged PRs more than doubled while the share reverted fell by more than 40%. We wrote about how we changed code review to get there, and how to adopt it:
Context
If AI writes most code at a leading lab, review becomes the main control point, and Anthropic's approach offers a template other teams may follow.
This is a first hand post from Anthropic's Claude developer account, and the figures are internal and unaudited. It follows the general release of Claude Code Review the day before.
Deep dive
On October 16, the ClaudeDevs account posted that Claude writes about 90% of Claude Code's code. It said that from June to September, merged pull requests more than doubled while the share that was reverted fell by more than 40%, and linked a post on how the team changed code review to get there and how others can adopt it.
The linked blog post describes how the Claude Code team handles review now that AI writes most of its code. The day before, Anthropic made its Code Review product generally available for Team and Enterprise plans, with Quick, Standard and Deep review levels, as covered in the October 15 deck.
On October 13, Anthropic said agents had pushed it to more than 30,000 merged code changes a day, leading it to build its own source control system, as covered in that day's deck.
The 90% figure is a share of code written, not a measure of how much human review or direction each change gets, and the revert rate is one indicator of quality among many. Anthropic did not publish raw data behind the numbers.
What to expect next
Watch whether other companies report similar shares of AI written code and whether their revert and bug rates hold up as volume grows.
Also watch adoption of Claude Code Review among enterprise teams, and whether Anthropic publishes more detailed quality data. Critics will look for evidence on whether review keeps pace with the volume of AI written changes over time.