AI Identifies Authors From 150 Words

A current-generation LLM (Anthropic’s Claude Opus 4.7) can attribute short, unpublished text excerpts to a real individual reliably from roughly 125–150 words, even across registers and drafts. The capability works without account memory and in Incognito or API settings, meaning stylistic fingerprints alone can suffice. — If widespread, this capability undermines online anonymity and will reshape debates about free expression, whistleblowing, platform policy, and legal protections for anonymous speech.