Slack is officially worth $5.1 billion after raising a monster $250 million round

Slack CEO Stewart Butterfield

It's official: Workplace messaging app Slack is worth $5.1 billion (£3.8 billion) after raising a $250 million (£184 million) funding round from SoftBank's Vision Fund, Accel, and other investors.

The new valuation is up from $3.8 billion (£2.8 billion) on Slack's last round and takes the firm's total funding to $841 million (£620 million).

Rumours about the new round began circulating in July, and we first saw the news via Bloomberg.

The company plans to use its new funding for "operational flexibility", and said it still has most of the funding it's previously raised, Bloomberg reported.

Slack launched in 2013, billing its work chat service as the end of email. It became the fastest startup to become a "unicorn" with a $1 billion valuation, and last week reported a major milestone: $200 million in recurring annual revenue. There were also rumours that Amazon was considering acquiring the firm, though a deal hasn't materialised.

Slack has more than 9 million weekly active users, up from 6.8 million in January.

Chief executive Stewart Butterfield said the firm would probably go public, but not until after 2018, according to The Financial Times.

The latest round shows the ready flood of private money available to fast-growing software startups. SoftBank revealed its $93 billion (£69 billion) Vision Fund in May and has this year gone on an investment spree, putting cash into troubled fintech startup SoFi, shared office space firm WeWork, and Indian ecommerce site Snapdeal, among others.

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