Slack hired investment bank Goldman Sachs as the lead underwriter for its highly anticipated initial public offering, Reuters reported Friday. Slack is talking with investment banks to help underwrite an IPO, which could end up valuing the chat and workplace-collaboration software maker as high as $10 billion, Reuters said, citing unnamed sources. In August, Slack raised $427 million in a private round of financing led by General Atlantic and Dragoneer. At the time, the investment valued the company at more than $7 billion.