Fun fact: that's called a generic trademark
OpenAI does worse than that. It tried to make GPT a trademark but USPTO rejected it. So it’s not even a trademark let alone a generic trademark.
https://tsdr.uspto.gov/documentviewer?caseId=sn97733259&docI...
When you call your product "(Chat) Generative Pretrained Transformer" then I don't think you have a great defense against genericisation.
The legal history of these is interesting, lots of household names have lost their trademarks, and lots of seemingly generic names are still trademarked. This way to the rabbit hole -> https://en.wikipedia.org/wiki/List_of_generic_and_genericize...