OpenAI completed a $6.6 billion secondary share sale, allowing current and former employees to sell stock at a record $500 billion valuation.

The deal, which included investors such as Thrive Capital, SoftBank, Dragoneer, Abu Dhabi’s MGX, and T. Rowe Price, involved about two-thirds of the $10.3 billion in authorized shares.

The sale follows a previous $1.5 billion transaction with SoftBank in November and solidifies OpenAI as the world’s most valuable privately held company, surpassing SpaceX.

Participation in the offer was limited to employees who had held shares for more than two years, and the lower-than-authorized uptake is being interpreted internally as a sign of confidence in the company’s long-term prospects, CNBC has reported.

The move also serves to retain talent amid growing competition in the AI sector, allowing employees to cash out without pursuing an IPO.