Do Em Dashes Mean AI Wrote It? What the Data Shows

On February 11, 2025, X user @PaulSkallas, who posts as LindyMan, wrote: "A shortcut for detecting if something is written with AI is they all use this symbol '—' throughout the writing... It's relatively rare when a human uses it... But AI chats love using it."

It reached 3.7 million views and 11,000 likes, according to Daily Dot's reporting. Writers and editors pushed back immediately in the same thread, pointing out that plenty of humans use the mark deliberately and often.

No AI provider was involved at any stage. This is a pattern one person noticed and posted about, not a technical claim any lab has ever confirmed.

Six chatbots given identical prompts produced anywhere from zero to nine em dashes each. Jonathan Bailey, a plagiarism and copyright analyst, kept his June 2025 test simple: identical prompts, six chatbots, count the em dashes in each response. The spread was enormous.

• ChatGPT: 8
• Microsoft Copilot: 8
• DeepSeek: 9
• Claude: 2
• Gemini: 0
• Meta.ai: 0

That range makes the rule unworkable even when comparing AI systems against each other, before you get anywhere near human writers, who have always used the punctuation mark on purpose.

Bailey's own conclusion went further. No single stylistic tell reliably separates AI from human text, and factual errors proved more diagnostic than punctuation habits.

OpenAI CEO Sam Altman announced in November 2025 that ChatGPT would finally honor custom instructions asking it to stop using em dashes, calling it a "small-but-happy win."

That's a personalization setting a user turns on, not OpenAI removing an embedded watermark, because there was never a discrete mechanism to remove.

Em dash frequency is a side effect of training data and fine-tuning. A real watermark is inserted deliberately and can be detected deliberately; a stylistic habit is neither.

In August 2026, Claude got a real invisible text watermark, a development with nothing to do with any single punctuation mark. Anthropic's support article describes weaving "an imperceptible watermark directly into the text itself" for models launched on or after August 2, 2026.

It names no punctuation mark, no phrasing habit, and no specific character as the mechanism. Independent research into the rollout has turned up no primary source confirming em dashes, phrasing tics, or hidden Unicode as the method.

The news broke on X the evening of August 10, 2026, through independent AI-news accounts rather than any Anthropic announcement of its own. The largest of those posts, from @M1Astra, reached 1.3 million views.

Within hours, a reply on that same thread from X user @Adrienne asked: "Isn't this just em dashes and calling everything load-bearing?"

It's a funny line, and it shows the confusion exactly. A confirmed watermark a provider deliberately embedded and a punctuation habit a stranger noticed are not the same kind of claim, even when they land in the same news cycle.

One claim circulating alongside the meme could not be confirmed: a Fast Company piece reportedly citing an unnamed Economist analysis, saying Claude specifically uses em dashes more than a human baseline.

Every attempt to reach the underlying source failed, since fastcompany.com returned an access error to each method tried. Nobody has produced the Economist analysis itself.

Worth setting beside it: in the only cross-model test with published numbers, Claude came in second lowest at 2. That doesn't disprove the claim, which compares Claude to humans rather than to other models, but it's the only checkable data anyone has.