Why does ChatGPT use so many em dashes?

ChatGPT and other chatbots use em dashes far more often than most people type them, which is why a page full of them now reads as a sign of AI text. Nobody outside the AI companies knows exactly why. The leading theories point to the books models learned from and to how handy the dash is for flowing explanations. If you want them gone, you can ask ChatGPT to avoid them or replace them afterwards.

Em dash, en dash and hyphen

Because the em dash takes extra effort to type, most people reach for a comma, a colon or parentheses instead. A chat model feels no such friction, and it uses the dash constantly.

Why chatbots overuse em dashes: the main theories

No AI company has published a definitive answer, so treat these as informed guesses.

• Older books in the training data. Software engineer Sean Goedecke argues that the habit arrived when AI labs began training on large collections of digitized print books, many from the late 1800s and early 1900s, when em dash use was near its peak. He notes that GPT-3.5 did not overuse the dash while later models such as GPT-4o did, which fits a change in training data between them.
• Polished writing as the model. Models are tuned toward edited, published prose such as journalism, essays and books, where em dashes are common. Casual writing like texts and comments, where people rarely type them, carries less weight.
• A dash does many jobs. An em dash can stand in for a comma, a colon or a pair of parentheses, so it lets a model add an aside or an explanation without restructuring the sentence. That suits a system built to explain things.

Goedecke also rejects some popular explanations, such as the idea that em dashes save tokens. The fair summary is that the habit came from training, and the companies have not said which part of it.

Does an em dash mean AI wrote it?

No. The em dash has been part of English for centuries, and writers from Emily Dickinson to today's journalists use it heavily. What stands out in AI text is the rate: several in a paragraph, in places where a comma would do. One em dash proves nothing, and judging someone's work on that basis is unfair.

Readers do notice, though. If your writing picked up the habit from an assistant, it is quick to undo.

How to stop ChatGPT using em dashes

On November 14, 2025, OpenAI CEO Sam Altman said that ChatGPT now follows custom instructions to avoid em dashes, after many users found it ignored the request (Digital Trends). Setting it up takes a minute:

1. 1

   Open custom instructions.

   In ChatGPT, open Settings, then Personalization, and find Custom instructions.

2. 2

   Add one line.

   For example: "Never use em dashes. Use commas, periods or parentheses instead."

3. 3

   Check the output.

   It mostly listens, but a long answer can still slip one in, so scan before you paste.

How to replace the em dashes you already have

Paste the text into the em dash remover. Each em dash becomes a comma or a spaced hyphen, number ranges become plain hyphens with no spaces, and curly quotes are straightened too.

A swap is a start, not a finish. Where the dash marked a big break, a period or a colon usually reads better than either, so give the result a quick read.