Block (Square, Cash App) rolled out BuilderBot — an AI agent that autonomously writes code, opens pull requests, and monitors CI. Already responsible for 15% of all production code changes. 1,500 PRs merged weekly. 200,000 operations daily.
How it works: engineer tags @builderbot in Slack with a task. The agent researches, writes code across the entire codebase, creates branches, opens PRs, and iterates. Tasks that took months now take days.
Why this matters:
- 1,500 PRs merged weekly. 200,000 operations daily
- Built on Goose (open-source, Linux Foundation) + MCP (co-developed with Anthropic)
- Engineer on Cash App can modify Square services they’ve never touched — agent knows the full codebase
Harness Theory validated: the human frames (Slack message). The agent ships (research → code → PR → CI → iterate).
