The Nasdaq and the S&P 500 had their worst day since June as investors worried about spending on A.I. infrastructure.

© The New York Times

Forget California’s billionaire wealth tax. The economist Natasha Sarin believes there are better ways to make billionaires pay up.

© The New York Times

Amazon became the latest tech company to announce swelling investments in A.I. amid stumbling share prices.

© Nathan Howard for The New York Times