Within 48 hours, the three biggest AI companies each made a move to own more of their stack. Anthropic blocked third-party tools from piggybacking on Claude subscriptions. Microsoft launched in-house foundation models to reduce its dependence on OpenAI. OpenAI bought a media company to control its own narrative. The mix-and-match era of AI — where you could freely combine models, tools, and distribution from different providers — is giving way to vertical integration and platform control.