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Slack became a $2.8 billion company in less than two years — and it's showing no signs of slowing down

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Slack

Slack, the wildly popular business messaging app, reached a $2.8 billion valuation in less than two years — and it's showing no signs of slowing down.

The company told us it now has 1.7 million daily active users, nearly 55% growth from just four months ago when it had about 1.1 million daily active users.

That's pretty impressive when you break it down by days — roughly 5,000 new active users have been added each  day. With that kind of growth, it's not hard to see the company's revenue growing even faster than it did in February, when it announced it's adding $1 million in new contracts every 11 days.

Those users are also turning out to be pretty heavy users too. On Monday, the company celebrated a new milestone of seeing one million concurrent users — that is, one million out of the 1.7 million daily active users were connected to Slack at the exact same time. 

Slack declined to say at what time or for how long the one million users were seen concurrently (its spokeswoman only told us, "No small feat and something they keep an eye on internally"). No less, the company seems to have thrown a small party to celebrate the new record, as seen in this tweet by Slack CEO Stewart Butterfield:

 

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Eugene Kim
Eugene is Business Insider’s Chief Tech Correspondent, where he leads coverage of Amazon. His reporting spans the company’s retail and logistics operations to AWS, Alexa, and its internal culture.Previously, he worked at CNBC, Fortune Magazine Korea, and Japan's Yomiuri Shimbun. He holds degrees from NYU and Columbia University’s Graduate School of Journalism.In 2022, Eugene reported on internal documents indicating that Amazon allegedly used deceptive tactics to enroll customers in Prime and made cancellation difficult. The Federal Trade Commission sued Amazon the following year, citing his reporting. The case ended in a record $2.5 billion settlement in 2025.His work has received multiple honors, including the SF Press Club’s Bay Area Journalism Award and SPJ NorCal’s Excellence in Journalism Award.Eugene lives in the Bay Area. Contact him via email at ekim@jkmperu.com, or Signal, Telegram, or WhatsApp at 650-942-3061. Use a personal email address, a nonwork WiFi network, and a nonwork device; here's our guide to sharing information securely.