Derivative works are typically things like language translations or film adaptions of a novel. A large language model is something like a probability breakdown of the order of word fragments in a body of text. It's a collection of statistics and math. It's different.
Now, can you get it to output a derivative work? Maybe. Is every output a derivative work? Maybe not.
Things like sports statistics and directories of phone numbers are not copyrightable. Maybe models fall into a similar category. Could be. It’ll be interesting to see how this shakes out over the next few years.
Now, can you get it to output a derivative work? Maybe. Is every output a derivative work? Maybe not.