A hyphen ( - ) is used to link parts of a compound word. This includes most dual heritages (Mexican-American), and all words in a compound modifier except "very" and adverbs that end in "ly." (The ...
On OpenAI’s developer message board, it’s speculated that the bot’s use of the em dash is due to its prevalence in the books and academic papers that OpenAI has ingested into its large language model.