Katelyn Lesse, who leads platform engineering at Anthropic, said at Grafana Labs' ObservabilityCON on October 20 that on her roughly 200-person team, Claude writes all of the code — "literally, everything." Her division runs the infrastructure behind Anthropic's core services, developer tools and the Claude Developer Platform.

Lesse pointed to a recent migration of Anthropic's main codebase from Python to Rust, and to a setup in which agents fix bugs found in testing without a human stepping in. Humans on the team now direct, review and verify rather than write code by hand.

The remarks describe her own team, not every engineer at Anthropic. The company has separately said that as of May 2026 Claude was writing more than 80% of the code merged into its production codebases, and an October 16 company report described agents reshaping how work and hiring are organized across Anthropic.