TanStack DB is a reactive client-side data store designed to enhance the capabilities of TanStack Query by introducing collections, live queries, and optimistic mutations. It leverages a TypeScript implementation of differential dataflow to provide sub-millisecond query performance, fine-grained reactivity, and robust transaction primitives. TanStack DB is backend-agnostic and incrementally adoptable, allowing integration with various data sources such as REST APIs, GraphQL, or custom sync engines. Developers can define typed collections, execute live queries with support for joins and aggregates, and perform optimistic mutations with lifecycle support. The library also offers adapters for frameworks like React and Vue, facilitating seamless integration into existing applications.