I typically use one four LLMs for search, depending on the task. I often enter the same prompt into two different ones to sort of double check the answers.

As an experiment, I entered the prompt: "What do you know about me?" into Claude, Perplexity, Gemini, and ChatGPT.

Claude and Gemini claimed to know nothing about me. ChatGPT knew some minor things, including one detail that is not on the web and I have no possible idea how it could have known that.

Perplexity knew really a lot and gave me an accurate summary with the following headers:

Professional Background

Personal Interests and Hobbies

Lifestyle and Habits

Technology and Entertainment Preferences

Recent Activities and Research Topics

Each of the categories was filled in pretty accurately. I'm not sure what the take away is here. I'm guessing Claude and Gemini could remember things about me if they really wanted to.