The Anthropic Leak

Claude Code Source Disclosure

Technical Deep Dive into the March 2026 Incident

What Actually Happened?

• Trending claim: "Anthropic leaked their entire source code"
• The Reality: Specifically the full source code of Claude Code (Agentic CLI)
• Status: Confirmed human error, not a security breach

The Data: What was exposed?

• ~512,000 lines of TypeScript source
• ~1,900 files in total
• 43 built-in tools & 44 feature flags
• 26 hidden slash commands
• Over 120 secret environment variables

The "Oops": How it happened

• Packaging Mistake: Accidentally bundled a .map file in the npm package
• R2 Linkage: The map file pointed to a ZIP archive on Anthropic's Cloudflare R2 bucket
• Accessibility: The archive was public and unencrypted

The Bun & .npmignore Factor

• Runtime: Anthropic uses the Bun runtime
• Default Behavior: Bun generates source maps by default
• Human Error: Forgot to add *.map to the .npmignore file
• Result: Shipped unobfuscated source alongside the production build

Why It's Permanent

• Viral Forking: Over 41,500 forks on GitHub immediately
• Mirrors: Hosted across decentralized repositories (IPFS/Torrents)
• DMCA Ineffective: The "Streisand Effect" in full force

A Rough Week for Anthropic

• Second Major Mishap: Occurred within days of another leak
• Model Leak: Unreleased model details (codenamed "Mythos" / "Capybara") left in a public repo
• Security Posture: Highlights systemic packaging/CI issues rather than infrastructure breaches

Key Takeaways

• Not a hack; a packaging pipeline failure
• Claude Code internals are now public knowledge
• No customer credentials or model weights were exposed
• A lesson in strict .npmignore and CI/CD validation