OpenAI has closed a secondary share sale totaling $6.6 billion, allowing current and former employees to sell stock at a $500 billion valuation, according to a person familiar with the transaction. The deal, first reported by Bloomberg, makes OpenAI the most valuable private company in the world, surpassing SpaceX at $456 billion. The buyers include Thrive Capital, SoftBank, Dragoneer Investment Group, Abu Dhabi’s MGX, and T. Rowe Price.

The sale was open to eligible employees who had held shares for more than two years. While OpenAI authorized up to $10.3 billion in shares, only about two-thirds of that amount ultimately traded. A person briefed on internal discussions said the lower participation is being viewed internally as a vote of confidence in the company’s long-term prospects and a sign that investor appetite remains strong even at the new valuation, which is up sharply from $300 billion earlier this year.

For employees, it is a rare chance to convert paper wealth into cash without an IPO. For OpenAI, it is a retention tool as competition for AI talent intensifies; Meta has reportedly offered nine-figure packages to poach researchers. Since the money goes to shareholders rather than the company’s balance sheet, it is not a conventional funding round, but it underscores OpenAI’s ability to attract capital as it pursues ambitious infrastructure plans.

The result lands as both a milestone and a puzzle: the world’s most valuable private company, yet with fewer insider shares changing hands than authorized. The sale fell short of the $10.3 billion authorized, according to CNBC, with insiders seeing the undersubscription as a sign of employee confidence and continued investor demand.