Just to clarify: This isn’t about memory being “on” or toggled in settings.

This was a controlled test involving GPT-5 and GPT-4o, which are supposed to have completely separate memory contexts per OpenAI’s documentation.

I typed a unique phrase into GPT-5, then deleted the chat.

I opened a new GPT-4o chat, with no shared history, and asked a vague follow-up.

GPT-4o quoted the exact phrase back.

In another test, it referenced material from an entirely different GPT-5 chat, never typed into 4o at all.

So this isn’t memory acting strange—it’s GPT-4o accessing GPT-5-only content, even from deleted sessions.

According to OpenAI:

“Chats with GPT-4o don’t currently use memory” and “Memory is unique to each model.”

If this is replicable, it’s not just a quirk—it’s a model boundary violation.

Happy to clarify details if others want to try reproducing.