The growth, announced Thursday, underscores increasing interest in the nearly four-year-old service, which is similar to Slack’s workplace chat app and Microsoft’s Teams collaboration tool. In October, Facebook said its business software had 3 million paid users.

Workplace is particularly popular with large companies that employ thousands of blue-collar workers, who typically aren’t given corporate email addresses, according to analysts. Big customers include Walmart, Dominos, and Starbucks. 

Like other consumer technology companies including Google and Amazon, Facebook believes it can make a big business in enterprise technology. Facebook’s Workplace software can cost companies $4 or $8 per employee depending on the plan. There’s also a free version that lacks certain security and IT monitoring features.

For now, revenue, which Facebook doesn’t disclose, is believed to be insignificant compared to the company’s overall annual sales of $70.7 billion.

Comparing the number of Workplace users with that of its competitors is difficult. The metrics companies disclose are inconsistent.

Facebook’s numbers, for example, take into account only paid active users and ignore free users. Meanwhile, Google said in March that its G Suite workplace apps had 2 billion monthly active users, which includes paid and free users combined. Slack said in October that it has 6 million “paid seats,” or the number of “engaged and active” users.

Julien Codorniou, vice president of Facebook’s Workplace unit, acknowledged that his company’s many past privacy blunders had initially hurt its effort to sell to corporations. But he emphasized that its service meets certain security standards and certifications that enterprise software companies typically adhere to. 

“Customers would not look at us like ServiceNow, Box, or IBM,” said Codorniou, mentioning three other enterprise technology companies. “We had to build the credibility.”

Also on Wednesday, Facebook said it had introduced new features for Workplace including a language translation tool and a tool for automatically captioning what people say during videoconferencing. The company also added the new feature Rooms, which lets users make video calls and interact in different channels akin to Slack.

Additionally, Facebook said that it has updated Workplace to work better with Facebook’s Portal video calling device so that the Portal can be used as a corporate videoconferencing tool. But while Workplace is compatible with competing video services like Zoom and Blue Jeans, Codorniou said some competing devices, which would include Amazon’s Echo Show, are not.