Claude Code's 512K-Line Source Code Was Hiding in Plain Sight on npm

On March 31, 2026, security researchers discovered that Anthropic had accidentally published 59.8 MB of Claude Code's proprietary source code — 512,000+ lines — through npm source maps left in the public package. This is Anthropic's second accidental disclosure in days, following the unintentional exposure of the internal 'Mythos' project details earlier in the week. Here's what was actually in the leaked code, what it means for users, and what vibe coders should do right now.