They've said it themselves multiple times: https://techcrunch.com/2018/08/21/slack-confirms-it-has-raised-427m-at-a-post-money-valuation-of-over-7-1b/ https://

They've said it themselves multiple times: https://techcrunch.com/2018/08/21/slack-confirms-it-has-raised-427m-at-a-post-money-valuation-of-over-7-1b/ https://techcrunch.com/2018/08/21/slack-confirms-it-has-rais... In previous rounds, Slack’s CEO and co-founder Stewart Butterfield has said that the company raises “opportunistically.” That is, it doesn’t have to raise money because it’s already making money and still has some in the bank, but as long as VCs are knocking, it’s worth taking the funding if it’s coming in at good valuations because you never know what might lie ahead. https://bits.blogs.nytimes.com/2015/04/16/is-slack-really-worth-2-8-billion-a-conversation-with-stewart-butterfield/ https://bits.blogs.nytimes.com/2015/04/16/is-slack-really-wo... And as a board member and a C.E.O., I have a responsibility to our employees, to our customers. And as a fiduciary, I think it would be almost imprudent for me not to accept $160 million bucks for 5-ish percent of the company when it’s offered on favorable terms. We don’t have an immediate use for that money. But it increases the value of our stock and can allow potential employees to take our offers, and it reinforces the perception for our larger customers that we’ll be around for the long haul. All of that stuff.