It's an opt out feature in the User Settings - Data Controls: Chat History & Training Save new chats on this browser to your history and allow them to be u

It's an opt out feature in the User Settings - Data Controls: Chat History & Training Save new chats on this browser to your history and allow them to be used to improve our models. Unsaved chats will be deleted from our systems within 30 days. This setting does not sync across browsers or devices.