Arianna Huffington, the former conservative commentator who co-founded and built the Huffington Post into one of the Web’s most prominent liberal media giants, said Thursday she will step down to focus on a new health-and-wellness startup.

Saying on Twitter she thought “HuffPost would be my last act,” Huffington, 66, said she would instead focus on new venture, Thrive Global, a yet-to-launch start-up focused on “ending the collective delusion that burnout is a necessary price for success.”

After co-founding the site in 2005, Huffington’s news giant quickly became one of America’s most-visited websites and led a new wave of opinion blogging, news aggregation and journalism crafted entirely for the Web. Her co-founders, Kenneth Lerer and Jonah Peretti, would later go on to spearhead the viral sensation Buzzfeed.

A left-leaning counterpoint to conservative news aggregators like the Drudge Report, “HuffPo,” as many called it, routinely repackaged stories and borrowed liberally from other news outlets, sparking tensions among traditional media but also creating a traffic-chasing model that has persisted and expanded today.

“In a way, it’s a golden age for consumers,” she said in 2010. “The Huffington Post is committed to the link economy.”

The site has since vastly expanded its staff across 14 countries devoted to original reporting, and won a Pulitzer Prize in 2012 for a series on wounded veterans and their families. It is the 156th most-visited website on the planet, Alexa data show, though its popularity has slipped. The site had 75 million unique visitors on desktop and mobile in the U.S. in June, down 18 percent from a year ago, Comscore data show.

Many Huffington Post writers and contributors are unpaid, and Huffington has argued that their visibility on a routinely viral news site is payment enough. Hundreds of staffers at the site last year voted to create a union.

Huffington stayed in leadership after AOL bought the site in 2011 for a landmark $315 million. But rumors swirled about her role after AOL was sold to Verizon last year for $4.4 billion. Huffington actively pursued other projects, including heavy promotion of her new book, “The Sleep Revolution: Transforming Your Life, One Night at a Time.”

In June, Huffington announced she was working on a new start-up but said her “primary focus” would remain her namesake site. But in a statement Thursday, she acknowledged she “simply couldn’t do justice to both companies” as Thrive Global’s prospects evolved.

Verizon last month also announced it would buy Yahoo, whose online news business closely parallels The Huffington Post’s. AOL chief executive Tim Armstrong said in a statement Thursday that “AOL and Verizon are committed to continuing (the Huffington Post’s) growth and the groundbreaking work Arianna pioneered.”

Huffington’s leadership has been called into question in recent months due to worries over her decision-making and focus on side ventures. In April, she was named to the board of directors for Uber, a potential conflict of interest given she was the top editorial executive for a site involved in covering Uber news. Soon after, the site rebuffed a story pitch that was critical of Uber.

The newsroom’s growing focus on sleep-related stories in line with Huffington’s new book also struck many as odd. Staffers there suggested Washington Post media columnist Erik Wemple “examine whether the finite editorial resources of the Huffington Post are being imprudently plowed into book promotion for the editor-in-chief.”

Thrive Global will be launched in November.