Enterprise messaging platform provider Slack Technologies, Inc.is said to be looking to raise a new round on a $4 billion valuation, according to multiple reports Wednesday.

The Wall Street Journal reports that the company is looking to raise $150 million, however, Bloomberg Business says that they are looking for between $150 million to $300 million.

Both publications quoted “people familiar with the matter” and Slack has declined to comment.

Slack’s most recent round was Series E on $160 million on a $2.8 billion valuation in April 2015.

At that time Chief Executive Officer Stuart Butterfield was forced to defend the valuation of Slack, the poster child of the unicorns (startups with a valuation of $1 billion or more) given it was the core of a story from Fortune in January 2015 which coined the phrase, saying that the round reflected what investors were willing to pay rather than any goal he set for the company.

“You can look at the valuation as an input or an output,” Butterfield said. “In this case it’s a little bit more of an output.”

Slack claims it had about 2.3 million daily users in February, up from 500,000 a year ago, and its headcount has risen to 369, and from 103 at the same time last year.

Up valuation

Presuming the reports are correct it would appear that Slack is defying the market yet again in asking for an up valuation, that is a higher valuation than it obtained in its last round, at a time more and more companies are raising funds on a down valuation, that is on a valuation less that what they had previously raised funds on.

The most prominent case of a down valuation in recent times has been Foursquare, Inc., although they are far from alone with around one in five mature startups raising money at lower valuations than in earlier rounds, according to a study by law firm Fenwick & West.

It’s not clear exactly what Slack wants to use the new round on other than continued growth and development, but that said they haven’t been quiet on those fronts following their last round, having rolled out support for Skype, an $80 million developer fund, support for emojis, and various other new features.

Slack has raised $340 million to-date from investors including Slow Ventures, The Social+Capital Partnership, Accel Partners, Andreessen Horowitz, Google Ventures, and Kleiner Perkins Caufield & Byers, Horizons Ventures, Index Ventures, DST Global and Institutional Venture Partners.

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