Engineering Culture, Tech Stack, and the $300M Infrastructure Modernization

PayPal operates one of the world's largest payment platforms -- processing $1.79 trillion in annual volume across 2,500+ microservices. The company is in the middle of a massive $300 million infrastructure restructuring (the "Q2 2025 Plan"), migrating from company-operated data centers to cloud, modernizing its technology stack, and investing heavily in ML/AI capabilities. This module covers PayPal's engineering culture, technical architecture, and what it means to be an engineer building at PayPal's scale -- essential context for system design interviews and technical discussions.