You may now have to scrutinize what you read on the internet (and event on print) more closely to determine if it’s the product of AI. Sam Altman has revealed on X that if you tell ChatGPT not to use em dashes in your custom instructions, the chatbot will now finally listen to you. Previously, ChatGPT would ignore your instruction and continue using em dashes even if you tell it not to.
Small-but-happy win:
If you tell ChatGPT not to use em-dashes in your custom instructions, it finally does what it’s supposed to do!
— Sam Altman (@sama) November 14, 2025
People are treating the presence of em dashes, especially if they’re used in abundance, as one of the biggest tells if something was written by large language models. Of course, just because a piece of text uses em dashes doesn’t mean it was actually written by AI, but people have become suspicious of any writing that uses the punctuation mark.
It’s not quite clear while generative AI models have the tendency to pepper the text they generate with em dashes. LLMs are trained on a vast number of books and online content, such as scientific papers, posts on public forums and articles like this. It’s possible that punctuation mark appears so often in training materials and isn’t flagged by AI trainers as something that the LLM should avoid using.
This article originally appeared on Engadget at https://www.engadget.com/ai/openai-says-chatgpt-will-listen-if-you-tell-it-not-to-use-em-dashes-140000927.html?src=rss
