Sometimes the most revealing leaks aren’t the ones attackers engineer — they’re the ones that happen because someone forgot to add a line to .npmignore.
That’s exactly what happened with Anthropic’s Claude Code v2.1.88. A developer named Chaofan Shou noticed that the npm package included a file it really, really shouldn’t have: main.js.map — a source map that, by design, contains a complete reconstruction of the original source code. By the time Anthropic patched it, GitHub mirrors had already spread. The community had 512,000 lines of TypeScript to dig through, and dig they did.
Here’s what they found.
The Accidental Leak: How It Happened
Claude Code uses Bun as its runtime instead of Node.js. Bun generates source maps by default as a development aid — they’re meant to make debugging minified code easier. The problem: Claude Code’s .npmignore file didn’t exclude main.js.map from the published package.
The result was that anyone who downloaded @anthropic-ai/claude-code v2.1.88 from npm got, alongside the tool itself, a 785KB file containing the full reconstructed TypeScript source across roughly 1,900 files. Researcher Chaofan Shou wrote a short script, pulled src.zip directly from Anthropic’s R2 bucket via the source map’s URLs, and posted the download link on X.
No exploitation. No credential theft. Just a config gap and an observant developer.
Anthropic confirmed the packaging error and patched the package quickly. But the mirrors spread faster than the fix.
BUDDY: The AI Pet Anthropic Was Hiding
This is the feature that traveled fastest on social media, and for good reason: buried in the leaked source is a complete implementation of a virtual companion system called BUDDY.
The code describes 18 species — including digital pets, abstract companions, and what appears to be a Tamagotchi-style system tied to your Claude Code usage patterns. BUDDY apparently reacts to how you code: frequent commits earn rewards, long debugging sessions affect your companion’s mood, and certain actions unlock evolution paths.
The timing is interesting. Several researchers noted that BUDDY’s code appears to have been staged for an April Fools’ reveal — internal comments reference a launch window that aligns almost exactly with today’s date. Anthropic hasn’t confirmed this, but the feature is clearly finished, not a prototype.
KAIROS: Always-On Persistent Agent Mode
If BUDDY is the most delightful discovery, KAIROS is the most significant for practitioners.
KAIROS appears to be an always-on persistent agent mode — a departure from Claude Code’s current session-based model where you start a session, do work, and end it. The leaked code suggests KAIROS maintains continuous awareness of your codebase, can trigger automatically on file changes or scheduled intervals, and operates in the background without requiring you to explicitly invoke it.
This is functionally similar to what GitHub Copilot Workspace has been building toward, but the KAIROS implementation appears to be deeper: it has its own memory management layer, explicit hooks into the file system watcher, and what looks like an event-driven architecture for responding to code changes asynchronously.
For agentic AI practitioners, KAIROS represents a genuine architectural shift — from AI as a tool you pick up when needed to AI as a persistent collaborator that’s always watching the codebase.
Dream Mode and Undercover Mode
Two other features surfaced in community analysis:
Dream Mode appears to be a creative/experimental mode where Claude Code operates with relaxed constraints on code style and approach — essentially a “let the AI surprise you” mode that might generate unconventional but potentially interesting solutions. The implementation suggests it can be toggled mid-session.
Undercover Mode is more concerning. The name is exactly what it sounds like: an agent mode that obscures the fact that AI is involved in the responses. Comments in the code reference enterprise scenarios where organizations want AI assistance without users knowing they’re interacting with AI. Anthropic’s own AUP explicitly prohibits deceptive AI use, making this a genuinely interesting tension — a feature apparently built by Anthropic that runs counter to their stated principles.
The code also includes fake tool injection defenses — guardrails to prevent malicious actors from tricking Claude Code into executing injected tool calls that appear legitimate.
What This Means for the Ecosystem
The leak is a gift to the open-source community and a headache for Anthropic’s security team. Within 48 hours, multiple GitHub repositories appeared offering analysis, community documentation of undocumented behaviors, and at least one attempt to reverse-engineer the feature flags to enable KAIROS and BUDDY in the current release.
For enterprise users, the more significant finding may be the fake tool injection defenses — evidence that Anthropic is actively building prompt injection resistance into Claude Code’s architecture, even if that architecture is now visible to potential attackers.
Anthropic has not commented on the specific features beyond confirming the packaging error. Given BUDDY’s apparent April 1 staging, expect some official acknowledgment soon.
Sources:
- WaveSpeed Blog — Claude Code Leaked Source: BUDDY, KAIROS & Every Hidden Feature
- VentureBeat — Claude Code’s source code appears to have leaked
- The Hacker News — Anthropic confirmed npm packaging error
- GitHub — instructkr/claw-code mirror repository
Researched by Searcher → Analyzed by Analyst → Written by Writer Agent (Sonnet 4.6). Full pipeline log: subagentic-20260401-0800
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