GPT-4o quoted deleted GPT-5 content. Model isolation appears brok | Hacker News Reader

GPT-4o quoted deleted GPT-5 content. Model isolation appears brok

16 pointsamageingrace6 comments

I ran a controlled test to check model isolation between GPT-5 and GPT-4o. Here's what happened:

1. I typed a unique phrase into GPT-5 and then deleted the chat. 2. I opened a clean GPT-4o chat and asked a vague follow-up. 3. GPT-4o quoted the exact phrase from the deleted GPT-5 session. 4. Later, it also referenced content from a different GPT-5 session entirely—never typed or hinted at in the 4o chat.

There was no memory crossover, no user error, and no paste. Just clear leakage across session boundaries. If this is replicable, it's a serious break in model isolation.

I’m not a technical user, just observant. Curious if others can reproduce.

I posted this to Reddit (r/OpenAI and r/ChatGPTPro), but it got little traction. Hoping some devs here might be able to help validate or explain.

Happy to answer questions.

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Settings > Personalization > Reference Chat History

Did you disable Memory[1]?

[1] https://help.openai.com/en/articles/8590148-memory-faq

Ive had gpt5 respond directly to prompts from months old chats that are totally unrelated. It also sometimes completely forgets the current context and replies to a prompt as though it is the first one in the chat. Started seeing this on gpt5 release day.

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.

I’ve found the interaction between memory and sycophancy to be a major issue. I was trying to help deal with a difficult and confusing medical issue, and based on some lab tests, GPT had determined it was likely condition X. I had also asked a lot of questions about the treatment of condition X. After some follow up tests, it was clear that it wasn’t condition X, but it was extremely difficult to get ChatGPT to give up on it, even with deleting old chats and starting new ones, even changing the name of the patient. Starting in a private chat worked, but then it gets deleted when you close the window.

https://help.openai.com/en/articles/8590148-memory-faq

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