Current and former OpenAI employees plan to sell approximately $6 billion worth of shares to an investor group that includes Thrive Capital, SoftBank Group Corp. and Dragoneer Investment Group, in a deal that values the ChatGPT maker at $500 billion, according to people familiar with the matter.The talks are early and the size of the share sale could still change, said the people, who asked not to be identified discussing private information. The secondary share investment is on top of SoftBank’...