Anonymity for prolific writers may be getting harder to preserve, after Vox writer Kelsey Piper said Anthropic’s Claude Opus 4.7 was able to identify her from a short, unpublished extract even when she had logged out, used incognito mode and stripped away saved preferences. According to SFist, the model correctly named her from about 125 words of a political column, raising fresh questions about how much personal style can reveal, even in supposedly anonymous settings.

Piper said she repeated the test in ways designed to rule out account-based clues, including asking a friend to run the prompt on another computer and sending the text through the API with no identifying context. In each case, she said, Claude reached the same conclusion. She also found that the model could sometimes identify her from other unpublished material, including a student report, a film review, fiction and a college application essay, suggesting that the system was responding to writing patterns rather than obvious topical hints.

Her findings, as described in her social media posts and in the SFist report, point to a broader concern for writers with visible digital footprints: a model may not need a name, username or browser history to make a plausible match. Piper said Claude and ChatGPT often offered explanations for their guesses that did not hold up well, leading her to suspect the models were working backwards from stylistic cues and then inventing a rationale after the fact.

She also tested friends with thinner online trails and found they were harder to identify, though not always fully anonymous. In some cases, she said, Claude appeared to lean on social connections and shared stylistic traits, circling a small cluster of associated writers rather than landing on a single clear answer. The overall picture, she argued, is that AI systems can already narrow down some authors from brief samples, and that the pool of people who remain difficult to identify may shrink as the models improve. That discussion comes as other coverage has framed Anthropic’s newer models as unusually powerful, including reports that a civilian-safe version of Claude Opus 4.7 has been released alongside claims about a far more capable, restricted system called Mythos.

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Source: Noah Wire Services