Claude Code
Anthropic's agentic coding tool, which its own team uses to write the tool's code. Its head has said publicly that Claude Code is written by Claude Code.
Claude, running inside Claude Code, writes the code changes that become the next versions of Claude Code, with engineers directing and reviewing. Each release is the harness used for the following round of development, and Anthropic reports the same shift across its whole codebase, where Claude now authors most merged code.
- Claude Code writes its own code changes
- Changes become next Claude Code versions
- Release becomes harness for next development round
- Claude Code writes its own code changes
- Changes become next Claude Code versions
- Release becomes harness for next development round
Why it is a road to recursion
A frontier lab's production harness is written by the model it serves, so model gains speed up harness development, and Anthropic presents this as progress toward recursive self-improvement.
Evidence
Head of Claude Code Boris Cherny told the Fortune Brainstorm Tech conference in June 2026 'Claude Code, 100% written by Claude Code', and Anthropic reports that more than 80% of code merged into its codebase as of May 2026 was authored by Claude, up from low single digits before February 2025.
Related loops
More self-modifying agents →- Coding agent edits its own code
- Scored child agents enter the archive
- Archived agents make later self modifications
- repeat
- Outer agent rewrites inner agent code
- Accepted rewrites become the incumbent agent
- Discovered agent becomes the outer loop agent
- repeat
- Best agent changes its own code
- Edited agent is benchmarked and archived
- Archived agent makes the next edit
- repeat