Slack’s business is reliable. Its IPO-less IPO plan is risky.

Slack, the workplace messaging tool that has become the platform of choice for industries like tech and media, is growing revenue at a rapid pace as it prepares to finally become a public company later this year.

Slack on Friday unsealed its paperwork with the SEC and revealed about $400 million in revenue in the fiscal year that ended this January — 80 percent more than it took in the year before. Revenue grew by about 110 percent in the year prior. The company is still not turning a profit, but losses have been relatively stable — read: not declining — over the last three years, at about $140 million. So its path to profitability is uncertain.

The company will offer the second test of a novel way to go public: a direct listing, which Recode first reported Slack was considering late last year. Rather than selling new shares in the company to Wall Street insiders in advance of the opening day of trading, Slack — as Spotify did a year ago — will publicly offer existing shares to anyone who wants to buy them on opening day.

That’s risky because selling stock to those insiders is meant to keep the price stable, as does the lockup that keeps shareholders from immediately selling their shares for a number of months. But the draw is that a direct listing is seen as more democratic — after all, anyone can buy shares — and reduces the cut of Wall Street banks, which some say have too much influence in the process.

Spotify’s direct listing is generally viewed by bankers and IPO experts as successful. The downside, which Slack acknowledges, is that it could make for a more volatile run on the stock market because Wall Street has not put up the guardrails around a company’s opening trades the way it typically does (although Spotify’s first year as a public company has not been out of the ordinary).

“The public price of our Class A common stock may be more volatile than in an underwritten initial public offering and could decline significantly and rapidly,” the company described as one of its risk factors, on the typically dour list of things that could go wrong.

Slack’s direct listing is in some ways riskier than Spotify’s because it is not a broadly known consumer company. Bankers have generally advised that a direct listing might make sense for brands like Airbnb, but Slack is gambling that enough regular people are familiar with their product that they will flock to the stock when trading begins. The company claims 10 million daily active users.

Slack is one of 2019’s most highly-anticipated “IPOs” (it’s not really an initial public offering, since there is no “initial” sale) because it has built a subscription software company of scale. Slack could be valued at as high as $20 billion in its opening days, which would easily make it the highest-valued enterprise company to go public in 2019.

That is, if it’s not bought first. Slack has been the target of acquisition interest in the past, and could very well find itself fielding suitors over the next few weeks.

One shareholder has an unusually large ownership grip on the company, the S-1 reveals. Accel Partners, an old-guard venture capital firm primarily known for its Facebook payday, owns almost a quarter of the company — which is pretty rare. Accel led both of Slack’s first two funding rounds when the company wasn’t even called Slack yet.

The company, led by founder Stewart Butterfield, grew out of a gaming startup called Tiny Speck that flopped — but with some money in the bank before it totally combusted. With the final dollars, Butterfield pivoted the company toward the messaging infrastructure that Tiny Speck used internally to communicate, and Slack was born.

This article originally appeared on Recode.net.