Omnicom Group has struck a $13.25 billion all-stock deal to buy rival Interpublic Group, creating the world’s largest advertising agency as traditional players look to better compete with Big Tech firms amid the accelerating use of AI. The deal, announced on Monday, is expected to attract regulatory scrutiny as it seeks to merge the world’s third-largest ad buyer. The combined company, led by Omnicom CEO John Wren, anticipates $750 million in annual cost savings.