Claude Code Is 90% AI-Written. Here's the 7-Layer Code Review System That Keeps It From Collapsing

Anthropic reports that Claude writes approximately 90% of Claude Code's own code. Between June and September, merged PRs more than doubled while reverts decreased by over 40%. The company implemented a 7-layer code review system to maintain stability at scale. This approach shifts the focus from human diff reviews to specific checks that identify potential failures. Meanwhile, separate explorations into automating legacy software highlight the challenges of working with licensed systems lacking APIs, as seen with Minicor.