Asianfin--Sierra, an AI startup co-founded by former Facebook CTO and Salesforce co-CEO Bret Taylor, is raising several hundred million dollars in a new funding round. According to insiders, the lead investor is growth-stage investor Greenoaks Capital. The latest round of funding is expected to more than triple the company's valuation, which stood at $1 billion during its January funding round. Sources anticipate Sierra's valuation will exceed $4 billion.