Slack boss Stewart Butterfield has poured cold water over Microsoft’s figures for Teams adoption during the coronavirus pandemic. 

The CEO was speaking to Market Watch about his own company’s spike in users and the inevitable comparison to Microsoft Teams seemed to get under his skin. 

Butterfield said the week starting March 9 was the “most productive” in his company’s history with a surge of new users turning into a “steep vertical” in two weeks. It took the platform four years to reach 10 million users, but from 10 March to 25 March, that number had grown by 2.5 million. 

There are a number of cloud-based services that have seen a big spike in users following the spread of COVID-19. Videoconferencing tools have become vital tools for people to connect with friends, family and work colleagues and Slack is also benefiting from the lockdown. It has, however, also increased the scrutiny upon its rivalry with Microsoft, which seems to irk Butterfield. 

“You probably sense the frustration in my voice,” he said on Market Watch. “Microsoft has made a huge push the past three years with a free service, but can you find a single Slack enterprise customer who has switched to Teams?”

“If Microsoft is such a competitive threat to Slack as it says, we would not have grown in sales and $1 million customers. I mean, 44 million is an impressive number, but that is out of 200 million Office 365 customers. That’s about a 20% adoption rate.”

Butterfield’s comments come just two weeks after he announced a Teams call integration on Slack, that suggested the two would bury the hatchet, but the CEO and his company have a history of firing barbs at the enterprise giant. Butterfield previously called Microsoft’s behaviour “unsportsmanlike” and in a tweet, Slack referred to it as a “boomer”. Despite recently going public, and also it’s rapid growth, Slack and Butterfield still see themselves as a startup taking on the corporate giant. 

“The smaller startup has an advantage against the large, established company because its focus is narrowed on doing one thing better,” Butterfield added. 

Cloud Pro has approached Microsoft for comment.