OpenAI has publicly acknowledged that the em-dash has become a "neon sign" for AI-generated text. They are updating their model to use it more sparingly, highlighting the subtle cues that distinguish human from machine writing and the ongoing effort to make AI outputs more natural and less detectable.

Medium's platform automatically converted double hyphens to em dashes for years, a stylistic preference of founder Evan Williams. This saturated its content with the punctuation mark, causing AI models trained on its vast corpus to replicate this quirk, effectively becoming a "tell" for AI-generated text.

In the age of AI, the new standard for value is the "GPT Test." If a person's public statements, writing, or ideas could have been generated by a large language model, they will fail to stand out. This places an immense premium on true originality, deep insight, and an authentic voice—the very things AI struggles to replicate.

Long before the em dash became associated with AI, it was criticized by literary figures for overuse. Jonathan Swift mocked it in the 18th century, and Lord Byron was panned for it in the 19th, showing a long history of grammatical purists viewing the mark as lazy.

As AI makes content creation easy, a cultural divide emerges. 'Lowbrow' culture imitates machines (e.g., using LLM-like speech). 'Highbrow' culture deliberately creates 'machine-resistant' art and communication to distinguish human effort and creativity from automated output.

The tendency for AI models to overuse em dashes may stem from their training data. To expand their knowledge, companies digitized millions of older books, including 19th-century classics where dash usage was at its historical peak. The models simply adopted this stylistic habit.

Once a staple of human literary expression, the em dash is now often perceived as a sign of AI-generated content. This shift has led to writers, like journalist Brian Vance, being wrongly accused of using AI, highlighting a new form of digital misinterpretation.

While the em dash is a known sign of AI writing, a more subtle indicator is "contrastive parallelism"—the "it's not this, it's that" structure. This pattern, likely learned from marketing copy, is frequently used by LLMs but is uncommon in typical human writing.

In an AI-driven world, unique stylistic choices—like specific emoji use, unconventional capitalization, or even intentional typos—serve as crucial signifiers of human authenticity. These personal quirks build a distinct brand voice and assure readers that a real person is behind the writing.