SiFive, a company founded in 2015 by the UC Berkeley engineers who created an open source chip design, has landed a $400 million oversubscribed round that values the company at $3.65 billion.

This deal is interesting for a bunch of reasons. For one, SiFive’s RISC-V open chip design is based on the RISC processor, not Intel’s x86 or ARM, the two major types of CPUs that currently feed Nvidia’s GPU computer system AI empire.

Also, Nvidia was investor in this round, alongside a long list of VCs, private equity, and hedge funds. The round was led by Atreides Management, founded by former Fidelity investor bigwig Gavin Baker. (Atreides was also an investor in Cerebras Systems $1 billion round). Other investors in the round include Apollo Global Management, D1 Capital Partners, Point72 Turion, T. Rowe Price, Sutter Hill Ventures, and others.

SiFive’s business model is like Arm’s was in years past — it licenses its chip designs to those who modify them for their own needs and does not sell the chips themselves. (In March, Arm changed its model when it launched the first-ever chip it manufactured, an AI chip, developed with Meta with customers including OpenAI, Cerebras, and Cloudflare.)

SiFive stands in rarified air with chip designs that are open, not proprietary, as well as neutral, not reliant on specific customers. In fact, SiFive hasn’t raised since March 2022, PitchBook estimates, when it brought in $175 million led by Coatue Management at a pre-money valuation of $2.33 billion. Intel Capital, Qualcomm Ventures, and Aramco Ventures were part of that round.

RISC-V has been, until recently, better known as a chip for smaller uses, like embedded systems. But with this cash and Nvidia’s attention, SiFive is moving into CPUs for AI data centers. SiFive’s designs will work with Nvidia’s CUDA software and its NVLink Fusion, a rack server system that lets different CPUs plug into Nvidia’s “AI factory.”

In other words, as rivals Intel and AMD seek to compete with Nvidia’s GPU, Nvidia is backing an 11-year-old startup that can design CPUs on an open and completely alternate technology.