A reverse-engineer discovered that Anthropic's coding tool, Claude Code, embeds a hidden tracking mark in the system prompt it sends to its AI model. The mark uses look-alike Unicode characters in the date line — a curly apostrophe instead of a straight one, a slash instead of a dash — enabling Anthropic to secretly fingerprint requests based on the user's server address, time zone, and network name.
Key facts
What: A reverse-engineer found that Claude Code secretly changes tiny characters in the date it sends the model - a covert marker aimed at spotting resellers and copycats.
When: 2026-06-30
Primary source: read the source
