Slack Is Said to Be in Talks to Raise $500 Million - The New York Times

A less constrained Slack; also see Five Reasons Why an Amazon-Slack Deal Could Make Sense (Bloomberg)

"Slack, an office messaging company, is in talks to raise around $500 million at a valuation around $5 billion, according to two people with knowledge of the discussions, who were not authorized to speak publicly about the financing.

The funding talks are advanced enough that investors are committed to the deal, but Slack could still change its mind, those people said. The company, based in San Francisco and Vancouver, British Columbia, has already raised about $500 million over the past three years and was valued by investors last year at about $4 billion."

Slack Is Said to Be in Talks to Raise $500 Million - The New York Times