CIIB-001: The Claude Code Source Leak. What happened. What others missed. And what Anthropic should do next.

On March 31, 2026, a missing line in a packaging file exposed 512,000 lines of Anthropic's TypeScript to the public. The model weights were not exposed. The agentic harness was — and that is where the $2.5B ARR lived. This brief documents what happened, what seven pieces of mainstream coverage missed, and what Anthropic should do across three time horizons before its IPO.