April 30, 2026
Anonymous? Not in that tone
Opus 4.7 knows the real Kelsey
Even strangers online are freaking out that AI can unmask you from a tiny writing sample
TLDR: Kelsey Piper says Claude Opus 4.7 could identify her from a tiny, unpublished writing sample, raising fears that hiding behind a username may soon be pointless. In the comments, people swung between panic and comedy as several said the model recognized them too—while others joked it might just be obsessed with guessing Kelsey.
Kelsey Piper’s warning shot landed like a privacy horror movie in the comments: she says Anthropic’s Claude Opus 4.7 guessed her identity from just 125 words of unpublished writing, even in an incognito window. That’s the scary part of the story—but the real spectacle was the community immediately turning it into a live-fire test of “oh no, it got me too.” Michael Lynch said the result was “blowing my mind,” then reported the model recognized a snippet from his unpublished book draft. Simon Willison tried his own post and got clocked almost instantly, with Claude basically rattling off his signature habits like an overenthusiastic detective.
And then came the drama: not everyone was ready to crown the machine the Sherlock Holmes of blogging. One commenter said they fed in their most-read post and Claude confidently claimed it was written by Kelsey Piper instead, which sparked the delicious possibility that Opus may have a few favorite “main characters” and just keeps guessing them. Another old-school hot take said this isn’t new at all—early versions of big language models were allegedly doing this years ago, even finishing text “in his voice” and signing it with his name.
The mood was a mix of awe, dread, and gallows humor. People weren’t just debating whether online anonymity is dying—they were stress-testing their own identities for fun, like it was a party game with terrifying stakes.
Key Points
- •Kelsey Piper says advanced AI models, particularly Claude Opus 4.7, can infer the author of relatively short text excerpts.
- •The article links this capability to concerns about the future practicality of online anonymity.
- •Piper reports that Claude Opus 4.7 identified her as the likely author of a 125-word unpublished passage she provided.
- •She says the same test in Incognito Mode, on a friend’s computer, and through the API produced the same result.
- •Piper writes that other models produced different guesses for the same passage, with ChatGPT naming Matt Yglesias and Gemini naming Scott Alexander.