There's more to sentience than just having a big enough database of human language in a neural network that a given AI can produce what sounds like coherent conversation when prompted. As I imply in my reply to bwanab, I believe there are at least two
bare-bones prerequisites to an AI being sentient and conscious as we understand the terms:
1. Continuity of input: The AI needs to be constantly "on", constantly receiving input of some sort, and constantly able to produce output, rather than being strictly limited to producing discrete responses to discrete stimuli.
2. Continuity of learning: In addition, the AI needs to be continually update its "mental model" of the world—in effect, constantly "learning" and re-training its neural network on the input it receives.
Now, again, these are not sufficient for an AI to be conscious by our understanding of consciousness. But I, personally, believe they are both necessary for it to be even worth starting to consider whether a given AI might be.
I also believe that unless we start in that direction extremely deliberately and with the intention of making something as human-like as possible, the first AIs that have some remote chance of being worthy of being considered "conscious" will not have a consciousness that we can easily recognize, because they will not be based in anything like the same kinds of fundamentals that we are...but that's likely a different discussion for a different day.