SAN FRANCISCO — Google co-founders Larry Page and Sergey Brin are stepping back from their day-to-day roles within the parent company, Alphabet, but plan to remain as board members and keep their ownership stakes.

The two tech billionaires said in a blog post Tuesday that they were ready to hand over the company reins to Sundar Pichai, who became CEO of Google in 2015 and will now take on the additional role of Alphabet CEO.

Alphabet is the umbrella corporation created in 2015 to hold Google and keep it structurally separate from the company’s “other bets,” such as the driverless car company Waymo, the life sciences unit Verily and other miscellaneous businesses.

Page had been serving as CEO of Alphabet, while Brin had been president of Alphabet. But they had been noticeably absent from company events in recent months, skipping entirely the company’s regular all-hands meetings this year, according to BuzzFeed News.

They wrote in the blog post that the company had “evolved and matured” in the two decades since its founding.

“Today, in 2019, if the company was a person, it would be a young adult of 21 and it would be time to leave the roost,” the two wrote.

“While it has been a tremendous privilege to be deeply involved in the day-to-day management of the company for so long, we believe it’s time to assume the role of proud parents — offering advice and love, but not daily nagging!” they added.

The two executives nurtured a squeaky clean “Don’t Be Evil” brand at Google since its founding, though its reputation has been tarnished in recent years by a series of scandals, including payouts to former executives accused of sexual misconduct.

Labor unrest has also erupted at Google’s offices, from the San Francisco Bay Area to Pittsburgh to Zurich. Four former Google engineers fired last week said Tuesday that they plan to file charges with the National Labor Relations Board, alleging unfair labor practices.

The company also faces an array of challenges on legal and regulatory fronts, from questions about the spread of conspiracy theories on its video service YouTube to an antitrust review of its power in the marketplace to a new European review of its data and privacy practices.

Still, Google remains one of the clearest success stories in the U.S. tech industry, emerging from a Silicon Valley garage in 1998 to become a web and advertising giant that bested a series of other search engines and is now the largest ad platform on the internet.

Alphabet took in about $150 billion in revenue for the 12 months ending Sept. 30, mostly from Google ad revenue, and reported that sales were still growing about 20 percent from a year earlier.

Ad sales have launched both men into extreme wealth. Page is worth about $62.6 billion, making him the seventh-richest person in the world, according to the Bloomberg Billionaires Index. Brin trails only slightly at about $60.7 billion, ranking 11th worldwide.

Both founders promised they plan to stay actively involved as board members and shareholders, and lauded Pichai for his leadership of the company.