Microsoft officially closed with a market capitalization above $4 trillion on Tuesday, October 28, 2025, following a groundbreaking restructuring agreement with OpenAI that reshapes the artificial intelligence landscape and signals investor confidence in the future of AI innovation.

The technology giant's shares surged 2% to close at $542.07, pushing its valuation to $4.04 trillion and cementing its position in an exclusive club alongside Nvidia as only the second company to reach this milestone.​

Partnership Evolution

The catalyst behind Microsoft's historic valuation stems from a newly finalized deal with OpenAI that fundamentally transforms their six-year partnership. Under the agreement, OpenAI transitions to a public benefit corporation valued at $500 billion, with Microsoft securing a 27% stake, worth approximately $135 billion, in the restructured OpenAI Group PBC. This represents a remarkable tenfold return on Microsoft's initial $13.8 billion investment in the ChatGPT creator.​

The restructuring removes critical constraints that previously limited OpenAI's capital-raising abilities while granting both companies unprecedented operational independence. Microsoft now retains exclusive rights to OpenAI's intellectual property—including models and products—through 2032, including developments beyond artificial general intelligence (AGI). However, Microsoft will lose access to OpenAI's research once independent experts verify AGI achievement or by 2030, whichever comes first.​

Strategic Flexibility

The most significant development lies in the newfound autonomy granted to both organizations. Microsoft can now pursue AGI development independently or with alternative partners, while OpenAI gains freedom to collaborate with third parties and serve non-API products on any cloud provider. Despite this flexibility, OpenAI has committed to purchasing $250 billion worth of Azure services, ensuring Microsoft maintains its position as the primary cloud infrastructure provider.​

The agreement establishes an independent expert panel to validate OpenAI's AGI claims and introduce accountability measures as AI technology approaches transformative capabilities. Once AGI confirmation occurs, the companies' revenue-sharing arrangements will conclude, marking the end of one partnership chapter and the beginning of another.​

This restructuring represents one of the most significant corporate realignments in technology history, balancing competitive innovation with collaborative momentum as the AI industry accelerates toward unprecedented capabilities.