You’re referring to a memory system. There’s a variety of memory techniques and so far chatgpt is one of the more practical, personal implementations. They might be doing simple RAG or something a little more clever. Simple RAG is a big first step but also has its limitations.

Short answer is yes, lots of people know how to do this. But in each use case, there could be a lot of tweaking to get it right. The tech is also getting better.