Current and former OpenAI employees are in early talks to sell about $6 billion of their shares to a group of existing backers that includes Thrive Capital, SoftBank Group Corp. and Dragoneer Investment Group, according to people familiar with the negotiations. The contemplated secondary transaction would value the ChatGPT developer at roughly $500 billion, though the size and terms of the deal could still change. At that price, OpenAI would leapfrog Elon Musk’s SpaceX to become the world’s most valuable closely held startup, underscoring investor conviction that generative artificial intelligence will drive the next wave of technology growth. The prospective valuation represents a sharp step-up from the $300 billion price tag attached to a separate $40 billion primary financing SoftBank has been arranging since March. Secondary sales allow venture-backed companies to give employees liquidity without pursuing an initial public offering, a useful tool as rivals such as Meta vie for AI talent. OpenAI’s rapid ascent follows the debut this month of its GPT-5 large-language model and an internal projection that revenue could more than triple in 2025 to about $12.7 billion, Bloomberg has reported.