The pace of the race to the top of Fortune's Unicorn List continues to hasten as startups raise ever-larger sums of money to fuel growth and expansion.

Airbnb, the well-known home rental service headquartered in San Francisco, has closed a new $1.5 billion funding round, according to reports from the Wall Street Journal and Financial Times. The round, which has been rumored for weeks, values the company at $25.5 billion—billions more than publicly traded neighbor Twitter (TWTR), which had raised far less ahead of its highly anticipated 2013 IPO, and hotel giant Marriott (MAR), which runs more than 4,000 properties around the globe.

At the time of its previous investment earlier this year, investors valued Airbnb at $20 billion. Among venture-backed startups, only Chinese phonemaker Xiaomi and car-hailing service Uber carry higher valuations.

Investors backing the young company this time reportedly include General Atlantic, Hillhouse Capital Group, Tiger Global Management, Kleiner Perkins Caufield & Byers, GGV Capital, China Broadband Capital, and Horizon Ventures.

"Airbnb is like a giant ship," CEO Brian Chesky told Fortune's Leigh Gallagher in her recent feature story on the 33-year-old chief executive. "As CEO I'm the captain of the ship." With the additional funds, Chesky just got a little more wind in his sails.

Want more? Read Fortune's complete coverage of Airbnb.

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