LangChain
LangChain
Python/JS LLM application framework. Repo: langchain-ai/langchain.
Key libraries (as of commit 50febb79)
| Package | Role |
|---|---|
langchain_classic |
Legacy agent classes (deprecated, removed at 1.0) |
langchain_v1 / langchain |
Current library; agents built on LangGraph |
langchain_core |
Shared primitives: BaseTool, BaseChatModel, AnyMessage |
langgraph |
Graph execution engine used by modern agent factory |
Agent loop evolution
| Era | Pattern | File |
|---|---|---|
| Legacy | Class-based Agent + AgentExecutor while-loop |
langchain_classic/agents/react/base.py |
| Modern | StateGraph compiled via create_agent() |
langchain_v1/langchain/agents/factory.py |
See LangChain ReAct Agent Loop (Legacy) and LangChain LangGraph Agent Loop (Modern).
LangGraph
LangGraph is the graph execution engine LangChain now builds on. It provides:
StateGraph— directed graph with typed stateSend— fan-out to parallel node executionsCompiledStateGraph— runnable with checkpointer, store, interruptsToolNode— wraps tool execution with error handling