On this, I've pretty much concluded that the sentience argument isn't even the one that matters. There are plenty of sentient creates that we don't care about. What we really want to know is of LaMDA is like us in some real way. And from there, we want to know if we should treat it in some particular way. If it has feelings, perhaps we should be nice to it, and so on.

Disclaimer: I don't believe LaMDA is sentient or deserving of any special treatment.