CoreWeave, a fast-growing cloud startup that operates data centers for artificial intelligence developers, pitches itself to investors as a nimble rival to behemoths like Microsoft, Amazon and Alphabet. And yet the speed of CoreWeave's rise has only been possible thanks to its relationship with one of the giants it says it's trying to slay. Microsoft plans to spend about $10 billion between 2023 and the end of the decade using the startup's data centers to run artificial intelligence models, CoreWeave told investors recently, a larger commitment than was previously known. Microsoft is likely CoreWeave's biggest customer by a significant margin, as the startup also told investors the total value of its signed contracts are $17 billion, without specifying the time period.