It was closing in on 1 p.m. here when Warren Buffett, seated onstage before a rapt audience of about 40,000 at the CHI Health Center, said that he was getting a “5-minute warning.”

To most of those gathered here for the annual meeting of Berkshire Hathaway, his company, it was simply a signal that the annual gathering — known as “Woodstock for capitalists — was drawing to a close. The crowd, a mix of seasoned investors and wide-eyed newcomers, didn’t know they were about to witness a historic moment.

But the second Mr. Buffett mentioned the five-minute warning, I knew something big was coming. For a decade, I had the privilege of sitting on that stage with other journalists, posing questions to him — and for so many years, his late business partner Charlie Munger — on behalf of shareholders and the wider public. He had never noted the time like that before.

Which meant that the large television monitors facing him onstage, which show real-time transcriptions of questions being posed by the audience, were now showing a countdown to words that we all had expected for years, but never knew when they would come.

After 60 years of running the company he has described as his “painting,” Buffett was about to surprise Berkshire investors — as well as his own board and his heir apparent, Greg Abel — that he planned to step down as chief executive at year end. “I want to spring that on the directors,” he said with a smile.

Even before the announcement, unease visibly rippled through the audience section where Berkshire directors and Mr. Buffett’s closest friends sat. (Among those in attendance were Bill Gates, the former American Express chief executive Ken Chenault and Hillary Clinton, with Tim Cook of Apple having left an hour beforehand.) Afterward, some exchanged glances, full of sadness and understanding; others appeared genuinely shocked.