The short answer: they absolutely do.

Anthropic's own Claude Code team uses Claude Code to build Claude Code itself. According to Anthropic's internal reports, 90% of Claude Code's codebase is now written by Claude Code, with engineers averaging 5 merged PRs per day — a 67% increase in per-engineer throughput since adoption.

The team uses auto-accept mode for fast prototyping, sets up autonomous loops where Claude writes code, runs tests, and iterates continuously, and delegates entire feature implementations to Claude in unfamiliar areas of their monorepo.

Claude Code hit 134k GitHub stars and runs on a terminal-first workflow — no clipboard gymnastics, no context-switching. It reads the project directly and acts in place.

So yes, Anthropic dogfoods Claude Code heavily. The tool that ships Claude Code was largely built by Claude Code itself.