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Constellation Energy Closes Calpine Acquisition, Becoming the Nation’s Largest Power Producer

Investors are reassessing the enlarged company given AI data-center contracts that lift long-term demand.

Overview

  • Constellation said it closed the $16.4 billion acquisition of Calpine on Jan. 7, broadening its generation mix across nuclear, natural gas, and geothermal assets.
  • The combined platform totals about 55 gigawatts of zero- and low-emission capacity, positioning the company as the largest U.S. electricity producer.
  • S&P Global affirmed Constellation’s BBB+ issuer rating and upgraded Calpine to BBB+, citing its role as a core subsidiary.
  • The company signed multiple long-term power purchase agreements with hyperscalers in 2025 to supply always-on power for AI data centers.
  • Shares have risen roughly 280% over three years yet sit about 15% below the 52-week high, prompting fresh valuation scrutiny in recent coverage.