A Google engineer stated that Lamda (chatbot) was sentient

It was in headlines all over. Google I think put him on suspension.

It didn't seem from the chat that Lamda WAS sentient to me. He went along with the prompts of the engineer and said he was sentient and elaborated. Mental Outlaw pointed out that the engineer didn't challenge the chatbot on the question, and supposed that if the engineer had been like, "You're not sentient you're an AI" the chatbot would have gone along with that and agreed (not that a chatbot would definitely even know if it WAS sentient or not, and not that a chatbot can't be sentient just because it's also a bot).

The question, though, is if AI is sentient, must we then treat it differently, ie as we would any sentient being? How can we know if an AI IS sentient?