Today, OpenAI is revealing their research on the issue, and can reveal that this was indeed real. Starting with GPT-5.1, the models did definitively prefer using «goblins» in their replies.
The culprit was the «nerdy» personality, which debuted with the launch of the 5.1-model and had increased «goblin»-mentions by 175% and «gremlin» by 52%. And by GPT-5.4, «goblin»-use had balloned by 3,881.4%, causing consternation at OpenAI.
The error seems to stem from rewarding a «playful style» with creature references, and this has since propagated through later releases.
The «nerdy» personality was retired in March after GPT-5.4 was released, but goblins snuck into the training data for GPT-5.5, too — forcing the system prompt to «Never talk about goblins, gremlins, raccoons, trolls, ogres, pigeons, or other animals or creatures unless it is absolutely and unambiguously relevant to the user’s query.»
Read more: OpenAI on goblins. On the system prompt: Gizmodo, Business Insider, and Ars Technica. Discussion on r/ChatGPT.