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While building memory systems, we realized their size grows fast. Session notes, temporary context, chat history - everything starts accumulating and bogging down the system. This pollutes search results and increase storage costs. Not every memory needs to persist forever. In this cookbook, we’ll go through how to use short-term vs long-term memories and see where it’s best to use them.

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Overview

By default, Mem0 memories persist forever. This works for user preferences and core facts, but temporary data should expire automatically. In this tutorial, we will:
  • Understand default (permanent) memory behavior
  • Add expiration dates for temporary memories
  • Decide what should be temporary vs permanent

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Setup

from mem0 import MemoryClient
from datetime import datetime, timedelta

client = MemoryClient(api_key="your-api-key")
Import datetime and timedelta to calculate expiration dates. Without these imports, you’ll need to manually format ISO timestamps—error-prone and harder to read.

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Default Behavior: Everything Persists

By default, all memories persist forever: 
# Store user preference
client.add("User prefers dark mode", user_id="sarah")

# Store session context
client.add("Currently browsing electronics category", user_id="sarah")

# 6 months later - both still exist
results = client.get_all(filters={"user_id": "sarah"})
print(f"Total memories: {len(results['results'])}")
Output: 
Total memories: 2
Both the preference and session context persist. The preference is useful, but the 6-month-old session context is not.

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The Problem: Memory Bloat

Without expiration, memories accumulate forever. Session notes from weeks ago mix with current preferences. Storage grows, search results get polluted with irrelevant old context, and retrieval quality degrades.
Memory bloat degrades search quality. When “User prefers dark mode” competes with “Currently browsing electronics” from 6 months ago, semantic search returns stale session data instead of actual preferences. Old memories pollute retrieval.

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Short-Term Memories: Adding Expiration

Set expiration_date to make memories temporary: 
from datetime import datetime, timedelta

# Session context - expires in 7 days
expires_at = (datetime.now() + timedelta(days=7)).isoformat()

client.add(
    "Currently browsing electronics category",
    user_id="sarah",
    expiration_date=expires_at
)

# User preference - no expiration, persists forever
client.add(
    "User prefers dark mode",
    user_id="sarah"
)
Expected behavior: After 7 days, the session context automatically disappears—no cron jobs, no manual cleanup. The preference persists forever. Mem0 handles expiration transparently.
Memories with expiration_date are automatically removed after expiring. No cleanup job needed - Mem0 handles it.
Start conservative with short expiration windows (7 days), then extend them based on usage patterns. It’s easier to increase retention than to clean up over-retained stale data. Monitor search quality to find the right balance.

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When to Use Each

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Permanent Memories (no expiration_date):

Use for:
  • User preferences and settings
  • Account information
  • Important facts and milestones
  • Historical data that matters long-term
client.add("User prefers email notifications", user_id="sarah")
client.add("User's birthday is March 15th", user_id="sarah")
client.add("User completed onboarding on Jan 5th", user_id="sarah")

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Temporary Memories (with expiration_date):

Use for:
  • Session context (current page, browsing history)
  • Temporary reminders
  • Recent chat history
  • Cached data
expires_7d = (datetime.now() + timedelta(days=7)).isoformat()

client.add(
    "Currently viewing product ABC123",
    user_id="sarah",
    expiration_date=expires_7d
)

client.add(
    "Asked about return policy",
    user_id="sarah",
    expiration_date=expires_7d
)

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Setting Different Expiration Periods

Different data needs different lifetimes: 
# Session context - 7 days
expires_7d = (datetime.now() + timedelta(days=7)).isoformat()
client.add("Browsing electronics", user_id="sarah", expiration_date=expires_7d)

# Recent chat - 30 days
expires_30d = (datetime.now() + timedelta(days=30)).isoformat()
client.add("User asked about warranty", user_id="sarah", expiration_date=expires_30d)

# Important preference - no expiration
client.add("User prefers dark mode", user_id="sarah")

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Using Metadata to Track Memory Types

Tag memories to make filtering easier: 
expires_7d = (datetime.now() + timedelta(days=7)).isoformat()

# Tag session context
client.add(
    "Browsing electronics",
    user_id="sarah",
    expiration_date=expires_7d,
    metadata={"type": "session"}
)

# Tag preference
client.add(
    "User prefers dark mode",
    user_id="sarah",
    metadata={"type": "preference"}
)

# Query only preferences
preferences = client.get_all(
    filters={
        "AND": [
            {"user_id": "sarah"},
            {"metadata": {"type": "preference"}}
        ]
    }
)

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Checking Expiration Status

See which memories will expire and when: 
results = client.get_all(filters={"user_id": "sarah"})

for memory in results['results']:
    exp_date = memory.get('expiration_date')

    if exp_date:
        print(f"Temporary: {memory['memory']}")
        print(f"  Expires: {exp_date}\\n")
    else:
        print(f"Permanent: {memory['memory']}\\n")
Output: 
Temporary: Browsing electronics
  Expires: 2025-11-01T10:30:00Z

Temporary: Viewed MacBook Pro and Dell XPS
  Expires: 2025-11-01T10:30:00Z

Permanent: User prefers dark mode

Permanent: User prefers email notifications

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What You Built

A self-cleaning memory system with automatic retention policies:
  • Automatic expiration - Memories self-destruct after defined periods, no cron jobs needed
  • Tiered retention - 7-day session context, 30-day chat history, permanent preferences
  • Metadata tagging - Classify memories by type (session, preference, chat) for filtered retrieval
  • Expiration tracking - Check which memories will expire and when using get_all()
This pattern keeps storage costs low and search quality high as your memory store scales.

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Summary

Memory expiration keeps storage clean and search results relevant. Use expiration_date for temporary data (session context, recent chats), skip it for permanent facts (preferences, account info). Mem0 handles cleanup automatically—no background jobs required. Start by identifying what’s temporary versus permanent, then set conservative expiration windows and adjust based on retrieval quality.

Control Memory Ingestion

Pair expirations with ingestion rules so only trusted context persists.

Export Memories Safely

Build compliant archives once your retention windows are dialed in.