The messaging startup rakes in $250 million from SoftBank’s Vision Fund, significantly increasing its valuation. : The messaging startup rakes in $250 million from SoftBank’s Vision Fund, significantly increasing its valuation. Workplace messaging app Slack is now valued at $5.1 billion thanks to an investment from Japanese internet giant SoftBank. The company confirmed Monday that it raised $250 million from SoftBank and other investors, including the venture capital firm Accel Partners, in its most recent funding round. In total, Slack has raised $841 million from investors. The company was valued at $3.8 billion in April 2016.