Tim Cook is stepping down after nearly 15 years, leaving Apple worth almost $4 trillion. But the next CEO inherits more than a well-tuned machine. They inherit a fundamentally different job. As AI becomes the operating layer of business, the CEO role is being structurally rewritten, from steward of excellence to architect of adaptation. The new question is not "Can you maintain performance?" but "Can you build an organisation that learns faster than the world changes?"