Block (Square, Cash App) just rolled out BuilderBot — an AI agent that autonomously writes code, opens pull requests, and monitors CI across Block’s entire codebase. It’s already responsible for 15% of all production code changes. This isn’t a demo. It’s Harness Theory in production at enterprisescale.
An engineer tags @builderbot in Slack with a task description. The agent then autonomously:
1
Researches requirements and plans implementation
2
Writes code across the entire codebase — an engineer on Cash App can modify Square services they’ve never touched
3
Creates branches, opens PRs, monitors CI
4
Iterates based on feedback — picks up tickets from Linear and Jira
The key differentiator: BuilderBot understands Block’s complete technical context — every service, API, and coding convention. It’s not a generic code assistant. It’s an agent with institutional knowledge of the company.
This is Harness Theory at scale. The human frames (Slack message with task description). The agent executes (research → code → PR → CI → iterate). 70/80 split — exactly what Anthropic’s 400K-session data showed. Block just proved it works at 200K operations per day.
The MCP + Goose Connection
BuilderBot is built on Goose — Block’s open-source AI agent framework, contributed to the Linux Foundation’s Agentic AI Foundation. Block also co-developed the Model Context Protocol (MCP) with Anthropic.
This matters because MCP is becoming the standard interface between agents and tools — and Block is one of its architects. BuilderBot isn’t just using the harness layer. It’s building the infrastructure that the harness layer runs on.
15% of all production code at a major fintech company is now written by an AI agent. 1,500 PRs merged per week. Tasks that took months take days. And it started with a Slack message. This is what the harness looks like when it’s not a framework — it’s a shipping machine. The 70/80 split is real. The human frames. The agent ships.
Gennaro is the creator of FourWeekMBA, which reached about four million business people, comprising C-level executives, investors, analysts, product managers, and aspiring digital entrepreneurs in 2022 alone | He is also Director of Sales for a high-tech scaleup in the AI Industry | In 2012, Gennaro earned an International MBA with emphasis on Corporate Finance and Business Strategy.
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