Enterprise collaboration app maker Slack raised $200 million, in a move it said “adds to our existing reserves and increases our ability to focus on an uncompromising long-term, strategic view”.

The round gives the company  a valuation of $3.8 billion, up from $2.8 billion in less than a year. Since launch it has raised $540 million.

Stewart Butterfield, CEO and co-founder, said: “As has always been the case, we are taking this opportunity to further secure our leadership position as we continue to execute on our ambitious growth plans.”

The company, which counts Harvard, LinkedIn, Dow Jones and Samsung among its clients, said it has 2.7 million daily active users and 800,000 paid users as of 1 April.

Slack offers a free service for small teams, as well as a ‘standard’ option of $6.67 per user per month which includes group calls, and a ‘super’ package that costs $12.50 per user per month and includes extra features such as support for external message and archival solutions.

According to TechCrunch, Slack’s daily user count and its paid seat count are up 3.5 times in just a year, with the average user spending 10 hours per weekday in the app.

It plans to launch an ‘enterprise’ option this year, which will also have organisation-wide reporting, metrics and analytics, among other features.

The round was led by Thrive Capital with participation by GGV, Comcast Ventures, and Slack’s existing investors such as Accel, Social Capital, Spark Growth and Index Ventures.

In December, Slack launched an $80 million fund for developers, backed by six of its investors.

The cash was meant to be a source of support for developers and small companies “deciding whether to make a bet on the Slack platform” to get started building apps.

Last week, Slack opened an office in Melbourne as its Asia-Pacific headquarters, noting that it’s where “a growing number of Slack customers reside”.