Constellation Energy agreed to buy Calpine for $16.4 billion, combining two of the country’s largest electricity generators at a time when their product is in high demand from tech companies. Including the assumption of debt,

U.S. nuclear power provider Constellation Energy on Friday agreed to buy privately held natural gas and geothermal company Calpine Corp for $16.4 billion, one of the biggest acquisitions in U.S. power industry history.

Constellation Energy Corp., an electricity provider whose stock has doubled over the last year on hopes it will help meet the voracious energy demand created by artificial-intelligence technologies, on Friday reached a $16.