The U.S. economy slowed at the end of 2025, capping a volatile year in which growth ultimately held firm, as resilient consumers and an A.I. investment boom helped keep growth on track despite tariffs, uncertainty and the longest government shutdown in history. Gross domestic product, adjusted for inflation, grew at a 1.4 percent annual rate in the final three months of the year, the Commerce Department said on Friday. That was down sharply from a 4.4 percent rate in the third quarter, partly because of the prolonged shutdown. For 2025 as a whole, measured from the end of 2024, G.D.P. increased 2.2 percent, compared with 2.3 percent the previous year. The numbers are preliminary and will be revised at least twice in the coming months.