That seems like a weird standard.

I would be happy enough with: only produces what it can verify with sources.

If you eg try to remember a court case (ie produce the reference via LLM token generation only), it's easy enough to check with your data whether it really exists. Similar for following links and other references.

If your data or sources are wrong, obviously your report about them will be wrong. But I wouldn't call that a hallucination.

Not to be tooo pedantic, but a bot that assigned 0 confidence to everything wouldn’t hallucinate.

A calculator either gets the right answer or doesn’t answer.

It wouldn’t have to be all knowing as long as it knew perfectly what it doesn’t know