This tutorial introduces LLVMCAS, a simple but high-performance Content-Addressable Storage library now available in LLVM, and shows how it makes builds faster and sounder. We cover the fundamentals of its design and tradeoffs, then walk through integrating a CAS into compiler tooling: making builds more deterministic, layering compilation caching on top, and fitting the pieces together in practice, with lessons from real-world use in Clang and Swift. We close with where compiler/CAS integration is headed. Aimed at compiler developers interested in build performance.