How do you install and set up LangChain?

LangChain is distributed as several pip packages. The minimal install for OpenAI-backed applications is:

pip install langchain langchain-openai
# For community integrations (vector stores, loaders, etc.):
pip install langchain-community
# For serving with REST API:
pip install langserve fastapi uvicorn

API credentials are passed through environment variables so they never appear in source code:

export OPENAI_API_KEY="sk-..."            # OpenAI
export ANTHROPIC_API_KEY="..."          # Anthropic / Claude
export LANGCHAIN_TRACING_V2="true"      # Enable LangSmith tracing
export LANGCHAIN_API_KEY="ls__..."      # LangSmith API key
export LANGCHAIN_PROJECT="my-project"   # LangSmith project name

A minimal "hello world" with LangChain:

from langchain_openai import ChatOpenAI
from langchain_core.messages import HumanMessage

llm = ChatOpenAI(model="gpt-4o-mini")
response = llm.invoke([HumanMessage(content="What is 2 + 2?")])
print(response.content)  # "4"

The package split is intentional: langchain-core contains stable base abstractions, langchain contains orchestration logic, langchain-openai and similar provider packages contain model integrations, and langchain-community contains third-party integrations that move faster.

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