Airbnb is losing its Wall Street-savvy CFO, getting its first COO and ruling out going public in 2018, delaying any payout for employees and early investors in the 10-year-old company.

In a blog post, Airbnb CEO Brian Chesky says Laurence Tosi, chief financial officer since July 2015, will be leaving the company to "dedicate his full time and energy to his investment fund, Weston Capital Partners, and dedicate time to the several boards he currently sits on."

Airbnb was last valued at $31 billion and has been a private company for 10 years -- once considered an eternity in the venture capital world, but no longer an outlier as more tech start-ups are staying private for longer.

Losing Tosi may raise questions about who can help take Airbnb public when it is ready. Tosi was CFO at Blackstone Group for nearly eight years and is widely seen as the adult in the room amid Airbnb's young founders. During his tenure at Airbnb, he helped turn the start-up profitable, as measured by earnings before interest, taxes, depreciation and amortization..

While Tosi is leaving the company, Airbnb is promoting its top female executive, Belinda Johnson, to the role of COO -- the company's first in its 10-year history.

A source tells CNBC that both Tosi and Johnson wanted the No. 2 role at Airbnb. "It ultimately came down to a difference in philosophy," the source says. "Belinda's Silicon Valley mentality toward organic growth versus LT's [a widely used nickname for Tosi] Wall Street mentality." Johnson won out.

Johnson spent more than a decade at Yahoo on its legal team before joining Airbnb in 2011 as general counsel. She was promoted to chief business affairs and legal officer in 2015 and she's been called the "Sheryl Sandberg of Airbnb."

When her promotion was announced earlier Thursday to Airbnb's leadership team, she received a standing ovation, according to someone in the room.