What caused the Claude Code source leak?

A missing .npmignore rule. The Bun build runtime generates source maps by default, and version 2.1.88 of the npm package shipped a 59.8 MB cli.js.map file holding the full source. A near-identical error happened at Claude Code's first launch in February 2025.

What is KAIROS in the Claude Code leak?

KAIROS is an unreleased always-on autonomous daemon found in the source, referenced 150 to 190 times across 61 files. It runs Claude Code as a background agent using periodic tick messages, GitHub webhooks, and 5-minute cron cycles, deciding on each tick whether to act or sleep.

Is it legal or safe to download the leaked Claude Code source?

No. Anthropic filed DMCA takedowns, and threat actors seeded fake archives with Vidar and GhostSocks malware plus a trojanized npm package. Downloading it risks both legal exposure and a malware infection. Read the analyses instead.

Did Anthropic fire anyone over the leak?

No. Anthropic called it "human error, not a security breach." Boris Cherny said the deploy process had manual steps and one was done incorrectly. No personnel were terminated.

· 8 min read

The Claude Code Source Leak: KAIROS, Undercover Mode and What 512K Lines Revealed

Anthropic leaked 512,000 lines of Claude Code on March 31, 2026. Here is what KAIROS, Undercover Mode, and one missing .npmignore line really revealed.

By Assaf BitonJune 28, 2026

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