Cost of revenue was $51mm this year for 10mm active users, so $5/user. Per their S-1 https://www.sec.gov/Archives/edgar/data/1764925/000162828019004786/slacks-1

Cost of revenue was $51mm this year for 10mm active users, so $5/user. Per their S-1 https://www.sec.gov/Archives/edgar/data/1764925/000162828019004786/slacks-1.htm#s8d6204acc583485eb9f4e9bf211b5e4a https://www.sec.gov/Archives/edgar/data/1764925/000162828019... : "Cost of revenue consists primarily of expenses related to hosting Slack and providing ongoing customer support for paid customers. These expenses include employee compensation (including stock-based compensation) and other employee-related expenses for customer experience and technical operations staff, payments to outside service providers, third-party hosting costs, payment processing fees, and amortization expense associated with internally-developed and purchased technology. We expect our cost of revenue to continue to increase in absolute dollar amounts as we grow our business and revenue." That amortization could be significant; it's likely that they're not spending $5 in hosting and devops alone. It may not be pennies, but it's way less than the cost of a car.