Short answers, pulled from the story.
Constellation Energy's stock dropped 56% in a single day on the 15th of September 2008 after reports emerged that the company had exposure to Lehman Brothers following that firm's bankruptcy filing. The New York Stock Exchange halted trading in Constellation that same day.
Exelon acquired Constellation Energy in a merger that was announced on the 28th of April 2011 and completed on the 12th of March 2012. As part of the deal, Constellation's energy supply business was rebranded as Constellation, an Exelon company, while Baltimore Gas and Electric became a regulated utility under Exelon Utilities.
Constellation Energy became an independent company in 2022 when Exelon split its utilities and power generation businesses. Baltimore Gas and Electric remained part of Exelon, while the generation business was spun off as the new independent Constellation.
In September 2024, Microsoft entered a contract with Constellation Energy to restart the undamaged nuclear reactor at Three Mile Island. In November 2025, the Trump administration announced a $1 billion federal loan to support the project.
Constellation is the leading nuclear power plant operator in the United States, with over 19,000 megawatts of capacity. Its plants are located across Illinois, New York, Pennsylvania, New Jersey, Maryland, and Texas.
In January 2025, Constellation Energy agreed to acquire natural gas and geothermal power provider Calpine for $16.4 billion, or $26.6 billion including debt, in a cash-and-stock deal. The acquisition closed in January 2026 after receiving approval from state and federal regulators.