LangChain Install & Auth

Overview

Set up LangChain SDK packages and configure provider authentication. Covers the modular @langchain/* package ecosystem for Node.js/TypeScript and langchain-* packages for Python.

Prerequisites

• Node.js 18+ or Python 3.9+
• Package manager (npm/pnpm or pip/poetry)
• API key from at least one LLM provider (OpenAI, Anthropic, Google)

Instructions

Step 1: Install Core Packages (TypeScript)

set -euo pipefail
# Core + one provider (pick what you need)
npm install @langchain/core @langchain/openai

# Additional providers
npm install @langchain/anthropic          # Claude models
npm install @langchain/google-genai       # Gemini models
npm install @langchain/community          # 100+ community integrations

# Common companions
npm install @langchain/textsplitters      # Text chunking for RAG
npm install @langchain/pinecone           # Pinecone vector store
npm install zod                           # Schema validation (structured output)

Step 2: Install Core Packages (Python)

set -euo pipefail
pip install langchain langchain-core

# Provider packages (install only what you need)
pip install langchain-openai              # ChatOpenAI, OpenAIEmbeddings
pip install langchain-anthropic           # ChatAnthropic
pip install langchain-google-genai        # ChatGoogleGenerativeAI
pip install langchain-community           # Community integrations

Step 3: Configure Authentication

# Create .env file (add to .gitignore!)
cat > .env << 'ENVEOF'
# OpenAI — https://platform.openai.com/api-keys
OPENAI_API_KEY=sk-...

# Anthropic — https://console.anthropic.com/
ANTHROPIC_API_KEY=sk-ant-...

# Google — https://aistudio.google.com/apikey
GOOGLE_API_KEY=AI...

# LangSmith (optional but recommended) — https://smith.langchain.com
LANGSMITH_TRACING=true
LANGSMITH_API_KEY=lsv2_...
LANGSMITH_PROJECT=my-project
ENVEOF

echo '.env' >> .gitignore

Step 4: Verify Connection (TypeScript)

import { ChatOpenAI } from "@langchain/openai";
import { ChatAnthropic } from "@langchain/anthropic";
import "dotenv/config";

// OpenAI
const openai = new ChatOpenAI({ model: "gpt-4o-mini", temperature: 0 });
const res1 = await openai.invoke("Say 'OpenAI connected'");
console.log("OpenAI:", res1.content);

// Anthropic
const anthropic = new ChatAnthropic({ model: "claude-sonnet-4-20250514" });
const res2 = await anthropic.invoke("Say 'Anthropic connected'");
console.log("Anthropic:", res2.content);

Step 5: Verify Connection (Python)

import os
from dotenv import load_dotenv
load_dotenv()

from langchain_openai import ChatOpenAI
from langchain_anthropic import ChatAnthropic

# OpenAI
llm = ChatOpenAI(model="gpt-4o-mini", temperature=0)
print(llm.invoke("Say 'connected'").content)

# Anthropic
llm2 = ChatAnthropic(model="claude-sonnet-4-20250514")
print(llm2.invoke("Say 'connected'").content)

Package Architecture

@langchain/core          # Base abstractions: Runnables, prompts, output parsers
  ├── @langchain/openai  # ChatOpenAI, OpenAIEmbeddings
  ├── @langchain/anthropic  # ChatAnthropic
  ├── @langchain/google-genai  # ChatGoogleGenerativeAI
  ├── @langchain/community  # 100+ integrations
  ├── @langchain/pinecone   # PineconeStore
  ├── @langchain/textsplitters  # RecursiveCharacterTextSplitter
  └── langchain             # High-level: agents, chains, tools

Every @langchain/* package depends on @langchain/core. You never import from langchain directly for base types -- always use @langchain/core for prompts, output parsers, messages, and runnables.

Error Handling

Troubleshooting Version Conflicts

# Check installed versions (all should share same minor)
npm ls @langchain/core

# Fix version conflicts
npm install @langchain/core@latest @langchain/openai@latest @langchain/anthropic@latest

Resources

• LangChain.js Docs
• LangChain Python Docs
• OpenAI API Keys
• Anthropic Console
• LangSmith

Next Steps

After successful auth, proceed to langchain-hello-world for your first chain.