Home-rental service Airbnb Inc. has completed one of the biggest private-funding rounds ever, raising $1.5 billion, in a deal that values the company at $25.5 billion, according to people familiar with the matter.

Leading the round were private-equity firm General Atlantic Inc., Hillhouse Capital Group of China and investment firm Tiger Global Management, which are collectively buying about a third of the shares allocated for the round, the people said.

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