The secondary share sale lets current and former OpenAI staff flog about $6.6 billion worth of shares, according to someone close to the matter. SpaceX was last valued at $400 billion in July.

Earlier this year, OpenAI was marked at $300 billion during a $40 billion financing led by Japan’s SoftBank Group. By the summer, executives were already eyeing a much higher valuation to sweeten an employee share sale, sources said.

Investors including Thrive Capital, SoftBank, Dragoneer Investment Group, Abu Dhabi’s MGX and T Rowe Price scooped up the stock. The deal, which had been floating around since August, was first revealed by Bloomberg.

OpenAI had told employees they could offload as much as $10 billion in stock, but many held back. The source said this showed confidence in the company’s future, adding that investors had actually wanted to buy more than $10 billion.

The transaction is the latest example of investors tripping over themselves to bet on AI, convinced that one winner in the sector will eventually be worth trillions.

Nvidia has already promised to sink up to $100 billion into OpenAI, with the understanding that the start-up will in turn deploy 10 gigawatts of computing grunt using Nvidia’s kit.

Since the launch of ChatGPT in late 2022, OpenAI’s annual recurring revenue has ballooned to $12 billion. The company now reckons it will hit $20 billion or more by the end of 2025, according to one insider.