It's not the "modern expert system", unless you're throwing away the existing definition of "expert system" entirely, and re-using the term-of-art to mean "system that has something to do with experts".
I don't know what the parent was referring to, but IMO "expert system" is one of the more accurate and insightful ways of describing LLMs.
An expert system is generically a system of declarative rules, capturing an expert's knowledge, that can be used to solve problems.
Traditionally expert systems are symbolic systems, representing the rules in a language such as Prolog, with these rules having been laboriously hand derived, but none of this seems core to the definition.
A pre-trained LLM can be considered as an expert system that captures the rules of auto-regressive language generation needed to predict the training data. These rules are represented by the weights of a transformer, and were learnt by SGD rather than hand coded, but so what?
Well, OK, perhaps not a declarative rule, more a procedural one (induction heads copying data around, and all that) given the mechanics of transformer layers, but does it really make a conceptual difference?
Would you quibble if an expert system was procedurally coded in C++ rather than in Prolog? "You see this pattern, do this".
