Twitter COO Adam Bain is stepping down amid the social media company’s struggles to add new users.

“After 6 years and a once-in-a-lifetime run, I let Jack know that I am ready to change gears and do something new outside the company,” he posted on Twitter on Wednesday, referring to Jack Dorsey, the company’s CEO.

Bain joined Twitter from Fox Interactive Media in 2010 as president of global revenue and partnerships. A year ago, he was promoted to chief operating officer when Dorsey was named permanent CEO. In part, Bain’s promotion was intended to provide more support to Dorsey, who has remained chief executive of Square, the payments company he co-founded in 2009.

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Twitter CFO Anthony Noto will take Bain’s role, the company said in a press release. Twitter will seek a new chief financial officer to replace Noto, who joined the company two years ago. Noto previously spent about 15 years at Goldman Sachs, with a brief stint as the National Football League’s CFO.

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While Bain is widely liked and respected both inside and outside the company, he’s had to help weather multiple challenges for the company including slowed user growth, investor pressure to lift its advertising business, a potential sale, and a recent announcement that Twitter would cut 350 jobs, or about 9% of its workforce.

Bain will help with the leadership transition in the coming weeks, the company said in a press release. While he hasn’t announced his next move, a source close to the situation told Fortune that he won’t be joining a competing company, unlike former Twitter head of product Kevin Weil, who joined photo-sharing app Instagram last year. Bain may even depart from the advertising business altogether, said the source.

Twitter’s stock price TWTR slipped by 3.3% to $18.50 in after-hours trading following the news.