Claude Wrote 80% of Anthropic’s Code as CI Load Rose 25-Fold

Summary

Anthropic disclosed that Claude writes about 80% of the company’s code. Engineers’ quarterly code output reached eight times the average level recorded from 2021 to 2025, and Claude also took on substantial parts of code review and merge approval. Its operating pattern differed from human engineering: it favored very small pull requests, submitted continuously around the clock, and drove a tenfold increase in the number of test cases. As a result, CI task volume increased 25-fold over six months and the system was nearly overwhelmed. Anthropic tried three fixes, including adding core capacity, sharding, and mandatory daily restarts, but none solved the problem. The company ultimately rebuilt the service as a distributed, stateless system after following a suggestion from Claude. The episode shows that AI-assisted coding can stress the software delivery systems around programming when code production is no longer limited by human work rhythms.