AI has become so effective at writing code and researching that the biggest constraint on developing new AI systems may now be the humans overseeing them, according to a new study by Anthropic.

In its report "When AI Builds Itself," published Thursday, Anthropic argued that Claude is already helping build future AI systems by writing code, running experiments, and assisting with research—a trend the company says could eventually lead to recursive self-improvement, where AI systems help design their own successors.

Claude now authors more than 80% of the code merged into its codebase, Anthropic said, and has helped engineers increase code output roughly eightfold since 2024.