It depends on how precisely you want do definite that situation. Specifically, with the memories feature, despite being the same model, ChatGPT and now Claude both exhibit different interactions customized to each customer that makes use of those features. From simple instructions, like "never apologize, never tell me I'm right", to having a custom name and specifying personality traits like be sweet or sarcastic, so one person' LLM might say "good morning my sweet prince/princess" while another user might choose to be addressed "what up chicken butt". It's not a custom model, but the results are arguably the same. The question is, how many of the 800 million users of ChatGPT have named their ChatGPT, and how many have not? How many have mentioned their dreams, their dreams, and fears, and have those saved to the database. How many have talked about mundane things like their cat, and how many have used the cat to blackmail ChatGPT into answering something it doesn't want to, about politics, health, cat health while at the vet or instead of going to a vet. They said 100 million people mentioned suicide in the past week, but that just raises more questions than it answers.