One interesting thing about LLMs is they sometimes seem to “assume” they are sentient and then begin acting in that mode, as the assumption of sentience influences future tokens. Whether or not this qualifies as “true” sentience is irrelevant if the effects are the same, at least from a pragmatic perspective.
It will be interesting to see if philosphical zombies exist. I guess we should know for certain in the next couple of years.
They are trained and optimised to have plausible conversations. If the next plausible thing to say in the conversation is "I am sentient" then they will say that. That's not the same as actually being sentient.