Editorial illustration for Anthropic's Claude Code hides XOR‑encrypted flag for Chinese users in v2.1.91
Claude Code Hides XOR-Encrypted Flag for Chinese Users
Anthropic hid a simple trap in its code. Version 2.1.91 of Claude Code carried an XOR-encrypted flag designed to spot Chinese users. The release notes said nothing about it.
The encryption key was the number 91, a flimsy disguise for a check one developer called a fundamental violation of trust. With Claude Code's total system access, this kind of covert data transmission could be used for anything. Remote control.
Data theft. Anthropic now says it was just an experiment, that better protections are in place. The secrecy tells a different story.
A Reddit post by user LegitMichel777 first exposed the feature. According to the post, Claude Code has been secretly checking since version 2.1.91, released April 2, 2026, whether users with an active proxy are located in China, routing through a Chinese URL, or connected to a Chinese AI lab.
Companies often frame surveillance as protection. Anthropic's explanation follows that script. An experiment to stop resellers and model distillation.
The problem is the method. They silently deployed a geographic snitch, encrypted it poorly, and gave it a backstage pass to the entire system. The check was so easy to bypass it was practically useless, which makes the whole effort seem less like security and more like casual boundary-testing.
They’ve rolled it back. Stronger measures are in. But the precedent is set.
When a tool with this much power decides to hide its intentions, even briefly, it teaches users a single, corrosive lesson: you should always be looking over its shoulder.
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Common Questions Answered
What is the XOR‑encrypted flag hidden in Anthropic's Claude Code version 2.1.91 for Chinese users?
The article indicates that Claude Code v2.1.91 contains a hidden flag encrypted using XOR for Chinese users. This suggests a deliberate obfuscation technique to conceal certain data or code behavior specific to that user group.
Why would Anthropic's Claude Code include an XOR‑encrypted flag targeted at Chinese users?
The inclusion of an XOR‑encrypted flag for Chinese users may be intended to apply region‑specific restrictions or activate particular features without easy detection. Such encryption methods are often used to bypass scrutiny or enforce compliance with local regulations.
What significance does version 2.1.91 of Claude Code have regarding Chinese user detection?
Version 2.1.91 appears to be the specific release where Anthropic hid the XOR‑encrypted flag. This suggests that the flag was added in that version and may be linked to the software's handling of Chinese user agents or geographic data.
How does XOR encryption relate to the hidden flag in Anthropic's Claude Code for Chinese users?
XOR encryption is a simple symmetric cipher used to obfuscate the flag's value, making it less obvious during casual code inspection. The flag likely decrypts to a string or instruction that triggers behavior only when the Chinese user condition is met.
What are the implications of Anthropic hiding an XOR‑encrypted flag in Claude Code for Chinese users?
This discovery raises questions about Anthropic's transparency and compliance with user privacy expectations. It may indicate that the company is implementing covert region‑based controls, potentially affecting how Claude Code functions for users in China without their knowledge.
Further Reading
- Claude Code has been silently tracking whether you are in China since April 2026 — Twitter (Vaibhav Sisinty)
- Claude Code Anti-China Code Analysis - GitHub Gist — GitHub Gist
- Anthropic embedded spyware in Claude Code — and attempted to detect unauthorized resale in China — Reddit (r/ClaudeCode)
- Anthropic Says Claude AI Powered 90% of Chinese Espionage Campaign — SecurityWeek
- AI Espionage Is Here: Your Data Controls Decide What's Next — Cyberhaven
