Here are the 20 fastest companies to reach a $2 billion valuation

The enterprise communication platform Slack recently became the fastest startup to reach a $2 billion valuation.

As CEO Stewart Butterfield told Business Insider in an interview, a bunch of forces came together to make it happen:

an unprecedented ability to companies to scale revenue

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an incredibly hot investment environment

the insane growth of Slack itself

"We've been crazily successful," Butterfield said. "Since we came back from the holidays, we doubled. That means that all the growth we had in 2014, we had again in a little over 3 months, and that's not usual. We had a fast rate of growth in the early days at small numbers, but it kept up. We've had over 5% week-on-week growth for the last 70 straight weeks - and that has just continued."

The financial information and technology provider PitchBook shared data with us about how Slack matches up with other Twitter, Pinterest, and other multi-billion-dollar startups:

Mike Nudelman/Business Insider

Read the full interview here.