This isn’t new at all. It’s used my name in the chain of thought since they released o1. OpenAI is more proud of the chain of thought in o3 and o4-mini so it’s making it more prominent, that’s why people are noticing it.

https://techcrunch.com/2025/04/18/chatgpt-is-referring-to-users-by-their-names-unprompted-and-some-find-it-creepy/