What does understanding mean? Is there a sensible model for it? If not, we can only judge in the same way that we judge humans: by conducting examinations and determining whether the correct conclusions were reached.

Probabilities have nothing to do with it; by any appropriate definition, there exist statistical models that exhibit "understanding" and "reasoning".

https://ai.vixra.org/pdf/2506.0065v1.pdf

Lays out pretty well what our current knowledge on understanding is