CoreWeave, an artificial intelligence startup backed by Nvidia, has signed a five-year contract worth $11.9 billion with OpenAI to provide cloud computing services ahead of its hotly-anticipated stock market launch, people familiar with the matter told Reuters on Monday. The deal will give OpenAI a stake in CoreWeave, which will issue shares worth $350 million through a private placement at the time of its initial public offering, the sources said, requesting anonymity as the discussions are confidential. CoreWeave will not receive any IPO proceeds as part of the private placement, the sources said.