Apple has dropped out of negotiations to participate in an OpenAI funding round expected to raise $6.5 billion.The iPhone maker's departure from the talks comes as a surprise and marks a rare instance of Apple investing in another major Silicon Valley company.Microsoft and Nvidia are still in talks to participate in the funding round, with Microsoft expected to invest around $1 billion.OpenAI is also undergoing the process of transitioning from a nonprofit into a for-profit company.