What Claude Code's Leaked Architecture Reveals About Building Production MCP Servers (2026)

Claude Code Source Code Leak: What Developers Found Inside By Shekhar — Founder, AgenticMarket. Written March 31, 2026, the day of the leak. I spent several hours reading the source today, so this is based on direct analysis rather than secondhand coverage. What happened: Anthropic accidentally shipped the full source code of Claude Code in an npm package. A debugging artifact called a source map pointed to a downloadable zip of 512,000 lines of TypeScript. Developers downloaded it, read it, and started posting what they found. What matters: The most significant thing in those 512,000 lines isn't a bug or a secret. It's the architecture. Claude Code isn't built on top of MCP. It is MCP — every capability, including Computer Use, runs as a tool call. KAIROS, an autonomous background agent mode, is compiled and feature-flagged. The product roadmap is now public. Why this is relevant to MCP server builders: the internal tools Anthropic built for Claude Code — authenticated, health-monitor