<overview LangChain Inc. maintains three layered open-source tools for building agents, plus LangSmith for observability. The stack, top-down: - Deep Agents (top layer, harness ) — batteries-included toolkit built on LangChain + LangGraph. Ships with planning, file management, subagent spawning, and memory out of the box. - LangGraph (middle layer, runtime ) — low-level orchestration for durable execution, custom control flow, and stateful workflows. LangChain agents run on top of LangGraph. - LangChain (bottom layer, framework ) — abstractions for models, tools, and the agent loop. Provider-…