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Google Researchers’ Attack Prompts ChatGPT to Reveal Its Training Data
(www.404media.co)
This is a most excellent place for technology news and articles.
They are spitting out, as in the quote above, "verbatim text", as in, word for word. That is copyrightable.
And that's not what you said. You said it has no memory. That's clearly wrong.
It’s only under copyright if it’s a significant portion of the work. Single sentences are not enough, unless it’s a short poem.