THE $10 BILLION CLUB: Meet the 8 most valuable startups in the US

Over the last several years, we've seen a rise in private companies valued at over a billion dollars - the so-called "unicorns."

But when too many startups became unicorns, a new class of startups emerged: "$4," or companies valued at over $10 billion.

These are the Ubers and Airbnbs of the world, the startups that steadfastly remain private companies as they seek more millions in funding at higher and higher valuations.

Below are the US startups valued at more than $10 billion.