LangChain Architecture

LangChain & LangGraph Architecture

Master modern LangChain 1.x and LangGraph for building sophisticated LLM applications with agents, state management, memory, and tool integration.

When to Use This Skill

Building autonomous AI agents with tool access
Implementing complex multi-step LLM workflows
Managing conversation memory and state
Integrating LLMs with external data sources and APIs
Creating modular, reusable LLM application components
Implementing document processing pipelines
Building production-grade LLM applications

Package Structure (LangChain 1.x)

langchain (1.2.x)         # High-level orchestration
langchain-core (1.2.x)    # Core abstractions (messages, prompts, tools)
langchain-community       # Third-party integrations
langgraph                 # Agent orchestration and state management
langchain-openai          # OpenAI integrations
langchain-anthropic       # Anthropic/Claude integrations
langchain-voyageai        # Voyage AI embeddings
langchain-pinecone        # Pinecone vector store

Core Concepts

1. LangGraph Agents

LangGraph is the standard for building agents in 2026. It provides:

Key Features:

StateGraph: Explicit state management with typed state
Durable Execution: Agents persist through failures
Human-in-the-Loop: Inspect and modify state at any point
Memory: Short-term and long-term memory across sessions
Checkpointing: Save and resume agent state

Agent Patterns:

ReAct: Reasoning + Acting with create_react_agent
Plan-and-Execute: Separate planning and execution nodes
Multi-Agent: Supervisor routing between specialized agents
Tool-Calling: Structured tool invocation with Pydantic schemas

2. State Management

LangGraph uses TypedDict for explicit state:

from typing import Annotated, TypedDict
from langgraph.graph import MessagesState

# Simple message-based state
class AgentState(MessagesState):
    """Extends MessagesState with custom fields."""
    context: Annotated[list, "retrieved documents"]

# Custom state for complex agents
class CustomState(TypedDict):
    messages: Annotated[list

3. Memory Systems

Modern memory implementations:

ConversationBufferMemory: Stores all messages (short conversations)
ConversationSummaryMemory: Summarizes older messages (long conversations)
ConversationTokenBufferMemory: Token-based windowing
VectorStoreRetrieverMemory: Semantic similarity retrieval
LangGraph Checkpointers: Persistent state across sessions

4. Document Processing

Loading, transforming, and storing documents:

Components:

Document Loaders: Load from various sources
Text Splitters: Chunk documents intelligently
Vector Stores: Store and retrieve embeddings
Retrievers: Fetch relevant documents

5. Callbacks & Tracing

LangSmith is the standard for observability:

Request/response logging
Token usage tracking
Latency monitoring
Error tracking
Trace visualization

Quick Start

Modern ReAct Agent with LangGraph

from langgraph.prebuilt import create_react_agent
from langgraph.checkpoint.memory import MemorySaver
from langchain_anthropic import

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Testing Strategies

import pytest
from unittest.mock import AsyncMock, patch

@pytest.mark.asyncio
async def test_agent_tool_selection():
    """Test agent selects correct tool."""
    with patch.object(llm, 'ainvoke') as mock_llm:
        mock_llm.return_value = AsyncMock(content=

Performance Optimization

1. Caching with Redis

from langchain_community.cache import RedisCache
from langchain_core.globals import set_llm_cache
import redis

redis_client = redis.Redis.from_url("redis://localhost:6379")
set_llm_cache(RedisCache(redis_client))

2. Async Batch Processing

import asyncio
from langchain_core.documents import Document

async def process_documents(documents: list[Document]) -> list:
    """Process documents in parallel."""
    tasks = [process_single(doc) for doc in documents]
    return await asyncio.gather(*tasks)

async def process_single

3. Connection Pooling

from langchain_pinecone import PineconeVectorStore
from pinecone import Pinecone

# Reuse Pinecone client
pc = Pinecone(api_key=os.environ["PINECONE_API_KEY"])
index = pc.Index("my-index")

# Create vector store with existing index
vectorstore = PineconeVectorStore(index=index, embedding=embeddings)