Slack hits 1 million users logged in at the same time by Kia Kokalitcheva @FortuneMagazine October 27, 2015, 7:42 AM EST E-mail Tweet Facebook Linkedin Share icons Slack, the workplace chat tool that’s been exploding in popularity, has just reached a new milestone: one million users being singed into the service at the same time. Co-founder and CEO Stewart posted a tweet about the feat on Monday, congratulating his employees for the company’s latest achievement. “Accounting for time zones, the 1M users represent a typical Slack mix across geographies,” a Slack spokeswoman told Fortune via email. Forget DAU. We're tracking "millisecond active users" now. pic.twitter.com/w3F7GKYlyB — Stewart Butterfield (@stewart) October 26, 2015 Slack isn’t the first company to start paying attention to metrics other than the traditional monthly or daily active user number. Snapchat co-founder and CEO Evan Spiegel said in May that the company has internally started to look at “hourly active users,” and Facebook recently celebrated having one billion users on its service in a single day. With that said, Slack’s official metric is still the daily active users number, which hit 1.7 million in October, according to the company.