This is sort of begging the question, because the only beings broadly considered sentient right now are humans. We’re the type specimen. So when people say something does or does not seem sentient, they’re basically opining on whether it seems like human behavior. While a rigorous physical definition would be incredibly useful, it’s not necessary for such comparisons. We make a lot of judgments without those.

It’s also sort of irrelevant that we have not clearly defined sentience because we have clearly defined how these large computerized language model systems work, and they are working exactly as they were designed, and only that way. Sentience might be a mystery but machine learning is not; we know how it works (that’s why it works).