Apollo Client 4.0 marks a significant advancement in GraphQL client technology, focusing on reducing bundle sizes, enhancing TypeScript support, and improving the overall developer experience. This version addresses community feedback by introducing an opt-in architecture for features like local state management, resulting in a 20-30% reduction in bundle size for many applications, and it modernizes build targets to support current JavaScript standards. Improvements in TypeScript include making types more discoverable and enforcing required variables, alongside a new dataState property that streamlines data status checks. Error handling has been refined with specific error classes, and the transition from zen-observable to RxJS enhances functionality with a broad ecosystem of operators. Apollo Client 4.0 also emphasizes compatibility with modern build tools and frameworks, offering a smoother migration path with comprehensive codemod tooling, ensuring an easier upgrade process for developers. This release is seen as a foundation for future developments in UI frameworks, thanks to its framework-agnostic core and cleaner TypeScript architecture.