What began as a philosophical question — how dangerous might artificial intelligence become? — has hardened into increasingly entrenched rival camps.

The Amazon-owned driverless car company is a distant second to Waymo. Its pitch to riders? Wine pop-ups, festival sponsorships and a car built to be filmed.

Brad Lightcap, a longtime leader, said he was starting a new venture. His exit from the artificial intelligence company is the latest in a series there.

As Waymo deploys more driverless cars to 15 U.S. cities and counting, its vehicles keep encountering new and unexpected situations that they have no script to handle.

At The New York Times’s Hard Fork Live event, Mr. Nadella addressed the backlash against artificial intelligence and President Trump’s comments about Americans sharing in the wealth of A.I. companies