All of them? If not, how to determine which ones?
There is a difference here between you and the machine
Looking at the LLM algorithms, they do appear to be next token predictors. Why do you ascribe something more to them when the algorithm is known?
Given we know that causal patterns are in the training data, and that LLMs are capable of embedding algebra, it is understandable that they appear to "reason", while we as humans can also describe the algorithm and mechanics actually at work here.
How does it determine how to respond to any prompt? Exactly. It might reasonably predict responses to those comments that, according to its black box, are somehow most likely to receive a reply. Different GPT instances prompted or trained to have different personalities would choose differently based on their priors and biases.
I'm pretty sure the vast majority of human beings are able to reason without really having the slightest idea as to how exactly they do it. Educated humans can use language to talk about reasoning in terms of logic, and even make logic engines out of doped silicon and whatnot, but as of now, none of us has any idea of how reasoning is implemented in the mass of fat and protein that's inside our heads.
Yet another case, many times we will respond (or not) to a questions with another question, to elicit deeper considerations. In my experience, GPTs will answer any question without thought, pun intended :]
The original question was, given that there were X comments which could be replied to on this page, how and why did the poster decide to respond to the one to which they responded, rather than either "all" (like ChatGPT would) or "none?"
If you mean feeding it the messages one at a time, then, sure, it will respond to each of them because that's what its default "goal function" is. (I assume that we're talking about a single "conversation" here so the context is retained – feeding it each comment out-of-context would be very unfair.)
If you prompt it to only reply to messages it considers "interesting" in some way, and return "I'll skip this" for the others, it would certainly do that.
Yes, GPT is code that only runs when you, erm… run it. It’s not an autonomous being that’s cut loose on the internet and given free reign to use as much compute resources as it wants, a la skynet, replying to random forum posts. But nobody’s really saying that it is, so it seems a strange argument to say “it’s just a next token predictor”, if by that you really mean “it only runs when you give it a prompt.”
The modality of GPT is that it responds to prompts, but the interesting question is “are the responses given a sign of intelligence?”. Saying “no, it’s just a next token predictor” is IMO a sign of a motte-and-bailey fallacy. Your motte is that it only works in response to prompts (trivially true and uninteresting), and your bailey is that it has no intelligence (very debatable and IMO false.)