Microsoft Corp. today announced that its Teams online collaboration service has now passed 20 million daily active users, causing stock in rival Slack Inc. to plunge Tuesday.

An increase of just over 50% on the 13 million users Teams had in July, the figure is notable not only because the service continues to grow rapidly but also because it’s a further surge ahead of Slack, which reported 12 million daily active users Oct. 29.

Slack shares dropped as much as 10% before closing the day down almost 8.4%, to $21.18. As CNBC noted, Slack shares are now down more than 18% since its New York Stock Exchange debut in June at $26 per share and down almost 50% from its first-day peak.

Despite figures showing that in a two-horse race, Microsoft is rounding the final corner furlongs ahead, Slack attempted to spin the announcement claiming that “engagement” was a more important metric.

“As we’ve said before, you can’t transform a workplace if people aren’t actually using your product,” a Slack spokesperson said today. “Slack continues to see unmatched engagement on our platform with 5+ billion weekly actions, including 1+ billion mobile actions. Among our paid customers, users spend more than nine hours per workday connected to our service, including spending about 90 minutes per workday actively using Slack.”

As for Microsoft, it didn’t even deem Slack worthy of mention.

“Teams brings together chat, meetings, calling, document collaboration, and workflow into a single app—and this unique combination is catching fire,” Jared Spataro, corporate vice president for Microsoft 365, said in a blog post. “In fact, today Teams has more than 20 million daily active users. What’s more, while these users start with simple text-based chat, they quickly move on to richer forms of communication and collaboration. For instance, last month Teams customers participated in more than 27 million voice or video meetings and performed over 220 million open, edit, or download actions on files stored in Teams.”

The new figures once again prove earlier predictions true in that Microsoft has a winning product in Teams. Launched with little fanfare out of a closed beta test in March 2017, it was predicted to be a success from day one.

A survey in December was the first to find what was later confirmed in hard numbers, that Teams had become more popular than Slack. That same survey also found that the adoption rate of Microsoft Teams was skyrocketing, with 41% of businesses saying that they plan to use Microsoft Teams by the end of 2020 versus 18% for Slack.

Image: Microsoft/Wikimedia Commons