Slack takes cues from social media and shows you messages that are most relevant

Key Points
  • Slack is venturing outside raw chronological order for ranking messages.
  • Highlights will appear in Slack channels and in the app's "All Unreads" window.
Stewart Butterfield, co-founder of Slack and Flickr
Mark Neuling | CNBC

Slack's corporate chat service is taking a page out of the Facebook and Twitter playbooks and adopting an algorithmic approach to showing messages.

The start-up, which is valued privately at $3.8 billion, released a feature on Wednesday that prominently displays the most relevant messages other people sent in the app while you weren't using it. With the new Highlights feature, Slack is moving beyond the conventional chronological ordering it has used since launching publicly in 2014.

Facebook and Twitter have both embraced algorithmic ranking to surface certain content in timelines for their users. Slack is revamping its product so that people don't have to spend time going through everything they may have missed.

Users of the paid service will see up to 10 messages deemed to be most relevant in the "All Unreads" section. Those messages will have a light yellow background inside the individual channels where they first appeared.

The feature becomes particularly useful for people who subscribe to numerous channels and have alerts flying at them from many different directions. For example, Highlights helped Noah Weiss, the head of Slack's growing search, learning and intelligence group, catch up on the most important activities across 100 channels after he returned from meetings with customers earlier this week.

"Welcome to how we use Slack at Slack," Weiss said in an interview with CNBC.

The system is personalized, taking into consideration factors like which users you engage with most often and which channels you most carefully follow. Recommendations will get better over time as Slack tracks your usage.

Highlights in Slack's All Unreads section.

Like other recommendation systems, Highlights uses machine learning to predict the messages that will be of most interest. But the system might not always be perfect. Slack is also letting users give feedback on Highlights recommendations with a simple thumbs up or thumbs down.

In recent months Microsoft has come out with a Slack competitor called Teams, and Google has introduced its spin on Slack called Hangouts Chat. Microsoft and Google both have other services for messaging while Slack fields just one product.

Slack, which is used by big companies including Capital One and IBM, has gained traction in recent years partly because it tends to result in less internal email communication. Weiss points out that Slack is more than an alternative to email because Highlights can alert you to interesting things in channels that you might not be following.

"With email, you can't say, 'Hey, Jordan, there's a really interesting email thread you're not a part of, but if you ask Amy, maybe she can BCC you,'" Weiss said.

Weiss's group previously introduced several updates to Slack's search feature, including identifying the people who frequently talk about a given theme in different channels. In the future, Slack could start using its data to spot trending topics across companies and even draw attention to channels where a conversation is suddenly spiking, Weiss said.

Slack has more than 1.5 million paid users and more than 5 million daily active users.