On September 12, 1997, Jiang Zemin’s report to the 15th Party Congress set goals for two dates. By the hundredth year of the Party, the economy would be more developed. By the middle of the century, the hundredth year of the People’s Republic, China would basically achieve modernization.
Chinese Wikipedia traces the Two Centenary Goals (两个一百年) to this report. On July 1, 2021, Xi Jinping declared: “We have achieved the first centenary goal.”