Quick answer If you need a Python library to build an AI agent that can run in production, start with LangChain for flexibility, CrewAI for team-style orchestration, or LlamaIndex if your focus is on data-centric retrieval. All three install with a single pip command, but they differ in abstraction level, runtime cost, and how easy they are to test inside a FastAPI service. What are the top Python libraries for building AI agents? The three most battle-tested optio...