Skip to main content
Memory in LangGraph enables agents to remember information across interactions, creating more contextual and personalized experiences.

​
Types of Memory

LangGraph supports two types of memory:
  • Short-term memory: Conversation state within a single thread (via checkpointers)
  • Long-term memory: Persistent storage across threads and sessions (via stores)

​
Short-Term Memory

Short-term memory is automatically handled through checkpointers and message state.

​
Message History

Use MessagesState or add_messages for conversation history: 
from typing import Annotated
from collections.abc import Sequence
from langchain_core.messages import BaseMessage
from langgraph.graph import StateGraph, add_messages
from typing_extensions import TypedDict

class ChatState(TypedDict):
    messages: Annotated[Sequence[BaseMessage], add_messages]

graph = StateGraph(ChatState)
The add_messages reducer maintains conversation history: 
from langgraph.checkpoint.memory import InMemorySaver

memory = InMemorySaver()
app = graph.compile(checkpointer=memory)

# First message
config = {"configurable": {"thread_id": "user-123"}}
app.invoke(
    {"messages": [{"role": "user", "content": "My name is Alice"}]},
    config,
)

# Later message - agent remembers Alice
app.invoke(
    {"messages": [{"role": "user", "content": "What's my name?"}]},
    config,
)

​
Trimming History

Manage message history length: 
from langchain_core.messages import trim_messages

def trim_history(state: ChatState) -> dict:
    """Keep only the last 10 messages."""
    messages = state["messages"]
    trimmed = trim_messages(
        messages,
        max_tokens=4000,
        strategy="last",
        token_counter=len,  # Use actual token counter
    )
    return {"messages": trimmed}

# Add as a node
graph.add_node("trim", trim_history)

​
Semantic Trimming

Keep important messages: 
from langchain_core.messages import filter_messages

def keep_important(state: ChatState) -> dict:
    """Keep system messages and recent user messages."""
    messages = filter_messages(
        state["messages"],
        include_types=["system", "user"],
        max_count=20,
    )
    return {"messages": messages}

​
Long-Term Memory

Long-term memory persists information across conversations using stores.

​
Store Interface

Stores provide key-value storage with namespaces: 
from langgraph.store.memory import InMemoryStore

# Create store
store = InMemoryStore()

# Compile with store
app = graph.compile(checkpointer=memory, store=store)

​
Storing User Preferences

from langgraph.store.base import BaseStore

def save_preference_node(state: State, *, store: BaseStore):
    """Extract and save user preferences."""
    user_id = state["user_id"]
    preference = state["detected_preference"]
    
    # Store in user namespace
    store.put(
        namespace=("users", user_id),
        key="preferences",
        value={"preference": preference},
    )
    
    return {"status": "saved"}

def retrieve_preference_node(state: State, *, store: BaseStore):
    """Load user preferences."""
    user_id = state["user_id"]
    
    # Retrieve from store
    item = store.get(
        namespace=("users", user_id),
        key="preferences",
    )
    
    preference = item.value.get("preference") if item else None
    return {"user_preference": preference}

​
Memory Store Pattern

Create a dedicated memory system: 
class MemoryState(TypedDict):
    messages: Annotated[Sequence[BaseMessage], add_messages]
    user_id: str
    memories: list[str]

def extract_memories(state: MemoryState, *, store: BaseStore):
    """Extract and store important information."""
    messages = state["messages"]
    user_id = state["user_id"]
    
    # Use LLM to extract facts
    facts = extract_facts_from_conversation(messages)
    
    # Store each fact
    for fact in facts:
        store.put(
            namespace=("memories", user_id),
            key=str(uuid.uuid4()),
            value={"fact": fact, "timestamp": datetime.now()},
        )
    
    return {}

def recall_memories(state: MemoryState, *, store: BaseStore):
    """Retrieve relevant memories."""
    user_id = state["user_id"]
    current_message = state["messages"][-1].content
    
    # Search memories
    items = store.search(
        namespace=("memories", user_id),
        query=current_message,  # Semantic search if supported
        limit=5,
    )
    
    memories = [item.value["fact"] for item in items]
    return {"memories": memories}

​
Vector Store Integration

For semantic search over memories: 
from langchain_community.vectorstores import FAISS
from langchain_openai import OpenAIEmbeddings

class VectorMemoryState(TypedDict):
    messages: Annotated[Sequence[BaseMessage], add_messages]
    context: str

# Initialize vector store
embeddings = OpenAIEmbeddings()
vector_store = FAISS.from_texts([], embeddings)

def store_memory(state: VectorMemoryState):
    """Store conversation in vector DB."""
    last_message = state["messages"][-1].content
    
    # Add to vector store with metadata
    vector_store.add_texts(
        [last_message],
        metadatas=[{"timestamp": datetime.now().isoformat()}],
    )
    
    return {}

def retrieve_context(state: VectorMemoryState):
    """Retrieve relevant context."""
    query = state["messages"][-1].content
    
    # Semantic search
    docs = vector_store.similarity_search(query, k=3)
    context = "\n".join([doc.page_content for doc in docs])
    
    return {"context": context}

​
Memory Architectures

​
Summary Memory

Summarize old messages to save context: 
def summarize_conversation(state: ChatState):
    """Summarize older messages."""
    messages = state["messages"]
    
    if len(messages) > 20:
        # Summarize messages 0-15
        old_messages = messages[:15]
        summary = llm.invoke(
            f"Summarize this conversation: {old_messages}"
        )
        
        # Keep summary + recent messages
        new_messages = [
            {"role": "system", "content": f"Previous conversation: {summary}"},
            *messages[15:],
        ]
        return {"messages": new_messages}
    
    return {}

​
Entity Memory

Track entities across conversations: 
class EntityMemory(TypedDict):
    entities: dict[str, dict]  # name -> properties

def extract_entities(state: State, *, store: BaseStore):
    """Extract and update entity information."""
    user_id = state["user_id"]
    message = state["messages"][-1].content
    
    # Extract entities with LLM
    entities = extract_entities_from_text(message)
    
    for entity_name, properties in entities.items():
        # Get existing entity
        item = store.get(
            namespace=("entities", user_id),
            key=entity_name,
        )
        
        # Merge properties
        existing = item.value if item else {}
        updated = {**existing, **properties}
        
        # Update store
        store.put(
            namespace=("entities", user_id),
            key=entity_name,
            value=updated,
        )
    
    return {}

​
Knowledge Graph Memory

Build relationships between entities: 
import networkx as nx

class GraphMemory:
    def __init__(self):
        self.graph = nx.DiGraph()
    
    def add_fact(self, subject: str, predicate: str, object: str):
        """Add a fact to the knowledge graph."""
        self.graph.add_edge(subject, object, relation=predicate)
    
    def query(self, entity: str, hops: int = 2):
        """Get related entities within N hops."""
        if entity not in self.graph:
            return []
        
        # Get subgraph within N hops
        nodes = nx.single_source_shortest_path_length(
            self.graph, entity, cutoff=hops
        )
        
        return list(nodes.keys())

# Use in node
def query_knowledge(state: State, *, graph_memory: GraphMemory):
    current_topic = state["current_topic"]
    related = graph_memory.query(current_topic)
    return {"related_topics": related}

​
Memory Management

​
Forgetting

Implement memory decay: 
import datetime

def clean_old_memories(store: BaseStore, user_id: str, days: int = 30):
    """Remove memories older than N days."""
    cutoff = datetime.datetime.now() - datetime.timedelta(days=days)
    
    # List all memories
    items = store.search(
        namespace=("memories", user_id),
        filter={},
    )
    
    # Delete old ones
    for item in items:
        if item.value.get("timestamp") < cutoff:
            store.delete(
                namespace=("memories", user_id),
                key=item.key,
            )

​
Memory Consolidation

Merge similar memories: 
def consolidate_memories(state: State, *, store: BaseStore):
    """Merge similar memories to reduce redundancy."""
    user_id = state["user_id"]
    
    # Get all memories
    items = store.search(
        namespace=("memories", user_id),
        filter={},
    )
    
    # Group similar memories (using embeddings)
    clusters = cluster_similar_memories(items)
    
    # Merge each cluster
    for cluster in clusters:
        merged = merge_memory_cluster(cluster)
        
        # Delete old memories
        for item in cluster:
            store.delete(
                namespace=("memories", user_id),
                key=item.key,
            )
        
        # Store merged memory
        store.put(
            namespace=("memories", user_id),
            key=str(uuid.uuid4()),
            value=merged,
        )
    
    return {}

​
Best Practices

  • Separate thread and cross-thread memory: Use checkpointers for thread state, stores for cross-thread data
  • Index your stores: Add indexes on frequently queried fields
  • Implement memory limits: Prevent unbounded growth
  • Use semantic search: Vector stores enable better context retrieval
  • Privacy considerations: Implement user data deletion
  • Test memory behavior: Verify memories persist and load correctly
  • Monitor memory size: Track storage usage per user

​
Next Steps

  • Add Interrupts to review memories before saving
  • Learn about Deployment for production memory systems
  • Explore Debugging to trace memory operations

Build docs developers (and LLMs) love

Get started for freeTalk to us