In a building called the Partnerplex on Google’s sprawling campus in Mountain View, California, I’ve been invited to hear a 51-second phone recording of someone making a dinner reservation.

As I listen to what sounds like a man and a woman talking, Google’s top executives for Assistant, the search giant’s digital helper, watch closely to gauge my reaction. They’re showing off the Assistant’s new tricks a few days before Google I/O, the company’s annual developer conference that starts Tuesday.

This could be the next evolution of the Assistant, Google’s rival to Amazon’s Alexa, Apple’s Siri and Microsoft’s Cortana. It sounds remarkably — maybe even eerily — human, pausing before responding to questions and using verbal ticks, like “um” and “uh.” It says “mm hmm” as if it’s nodding in agreement. It elongates certain words as though it’s buying time to think of an answer, even though its responses are instantaneously programmed by algorithms.

Built with technology Google calls “Duplex” — and developed by engineers and product designers in Tel Aviv, New York and Mountain View — the AI sounds as though the future of voice assistants has arrived.

Google is coy about the size of the rollout, but says it’ll be limited — all the company will say is it won’t be available to everyone using Assistant today. Nick Fox, vice president of product and design for Google Assistant and Search, and Yossi Matias, Google’s vice president of engineering, say the search giant wants to “proceed with caution” because it’s such a new technology.

“We think of it as, ‘What’s a perfect assistant?'” says Fox, a 15-year Google veteran. “When I want an assistant with me, it’s there. It’s always ready to help. I don’t worry about ‘Can my assistant do it or not’? My assistant can do anything I want it to do.”

Asked about these issues, Fox acknowledged that the folks at Google are learning about these things as they go.

That includes more voice options. There are six new ones, both male and female, that all speak with an American accent. One female voice is soft and soothing. A new male voice is a little deeper with a slight rasp.

Another update, due this summer, is a mode called Pretty Please that will require you to be polite when giving the Assistant commands. The goal is to reinforce good manners in children — and adults, too — by prompting them to say please and thank you.