ChatGPT now respects “no em‑dashes” custom instruction — why punctuation became an AI tell
ChatGPT will now respect "no em‑dashes" custom instructions — a small but revealing update OpenAI CEO Sam Altman announced that ChatGPT will finally follow custom instructions that ask the model not to use em dashes. Previously, users reported that the assistant ignored this preference and continued inserting em dashes frequently. Altman called the change a “small‑but‑happy win,” reflecting a tweak to how the model honors formatting guidance. Why does this matter? Many people have come to treat heavy em‑dash use as a quick heuristic for AI‑generated prose. While em dashes alone aren’t definitive proof of machine writing, their recurrent appearance in generative outputs made the punctuation a common "tell" among observers and journalists. Why LLMs might overuse em dashes Training data: Large models learn from diverse sources — books, articles…
