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Slack confirmed its plans for an IPO today by making public a securities filing that showed it is still growing quickly, even as it remains deeply unprofitable.

The high-flying workplace collaboration startup also said it would indeed use the direct listing method that Spotify used last year. In that case, stock is sold directly into the market and the company itself does not raise any money in the IPO.

As such, Slack will begin a process of testing investor interest to determine a potential initial stock price, as well as determining how many shares are likely to be available at the start of trading.

The company reported revenue of $400.6 million in its fiscal year 2019, up 82% from $220 million in FY 2018, and $105.2 million in FY 2017. At the same time it lost $138.9 million (2019), $140.1 million (FY 2018), and $146.9 million (FY 2017).

Slack says the losses are due to investments in growth opportunities, adding optimistically: “Our net losses have been decreasing as a percentage of revenue over time as revenue growth has outpaced the growth in operating expenses.”

Slack is the latest in a string of high-profile startups to test the public markets this year. Uber has valued its upcoming IPO at $84 billion, while Lyft went public at a $24 billion valuation but has since slumped.

And social image site Pinterest closed its first day of trading with a $13 billion valuation.

Slack says it has 10 million daily active users and 600,000 organizations using the collaboration platform, including 88,000 paid customers.

It was previously known that Slack had confidentially filed its IPO plans with the U.S. Securities and Exchange Commission.

The filing also revealed that four venture firms will be big winners in the Slack Sweepstakes: Accel is the biggest stockholder in Slack, with 119,928,410 shares (24% of the company); followed by Andreessen Horowitz with 66,523,324 shares; Social Capital with 50,853,362 shares; and SoftBank with 36,611,744 shares.

CEO Stewart Butterfield holds 42,324,937 shares and may buy another 915,204 shares in the coming days.

Slack now has 1,502 employees, up from 716 employees on January 31, 2017. It has offices in Australia, Canada, Ireland, India, Japan, and the United Kingdom.

The company also lists Microsoft as its “primary competitor,” while giving a nod to Alphabet, Cisco Systems, and Facebook. And Slack says it will continue to increase investments in artificial intelligence and machine learning as it seeks to bring more efficiencies and automation to its workplace customers.

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