Mem0 vs Letta vs Zep: Which Should You Use for Agent Memory?
Mem0, Letta, and Zep are the three most-adopted open-source memory layers for AI agents, and they solve fundamentally different problems. Mem0 is a universal memory API — add, update, delete, retrieve — designed to drop into any agent with minimal integration. Letta (formerly MemGPT) is a stateful agent operating system that manages memory in tiers the agent itself can edit, inspired by OS memory management. Zep (with its Graphiti engine) stores memory as a temporal knowledge graph, preserving when facts were learned and how they relate to each other. The right choice depends on what your agent needs: simple key-value memory (Mem0), self-managing agent state (Letta), or time-aware relational knowledge (Zep). All three are Apache-2.0 licensed and connect to the MCP ecosystem — though in different ways — and they differ in storage format, retrieval model, and how much agency the memory system itself has.
The pain: choosing wrong is expensive
You are building an AI agent that needs to remember things across sessions. You have heard of Mem0, Letta, and Zep — maybe also Cognee, LangMem, or PLUR — and the READMEs all say "memory for AI agents." How do you choose?
