I am not convinced hallucinations is a solvable problem in a single self contained model. In one hand we approach these things with the idea we are building a real intelligence modeled after our assumptions of our own brain. In the other we want them to not have any of the failings of the things they are being modeled after.

Humans mis-remember and make up things all the time, completely unintentionally. It could be a fundamental flaw in large neural networks. Impressive data compression and ability to generalize, but impossible to make "perfect".

If AI becomes cheap and fast enough, its likely a simple council of models will be enough to alleviate 99% of the problem here.