Upwind, a San Francisco startup that uses AI to secure cloud infrastructure, has raised a $400 million Series C round at a $3.8 billion valuation led by Bessemer Venture Partners, with participation from existing backers including Greylock Partners and Craft Ventures.

The round comes nine months after Upwind closed its previous $250 million financing at a $1.5 billion valuation .

The fresh funding, which has been in the works for months, nearly fell apart after Datadog attempted to buy the company, according to a person familiar with Upwind. Datadog is a publicly traded company that sells tools for monitoring how software runs, known as observability. It didn’t offer a premium above the $3.8 billion valuation set by venture capital investors, the person said, so Upwind decided to stay independent.

Four-year-old Upwind has grown rapidly amid rising AI-driven cybersecurity threats.…