The 4 types of memory every agent builder needs to understand
Most agent builders hit the same wall. Their agent performs brilliantly in demos, then forgets everything the moment the context window fills up. They reach for a vector database and call it a "memory system." It isn't.
Real agent memory has four distinct layers. Here's each one.
1. In-context storage
What your agent can see right now. Fast, perfectly accurate, completely ephemeral. When the window closes, it's gone. Treat it like working memory, only put what the current task needs.
2. External storage
Databases and vector stores the agent queries at runtime. Scales infinitely, but retrieval is never perfect. The chunking strategy and retrieval method matter far more than most builders realise.
Examples: Pinecone, Weaviate, pgvector, Qdrant, MongoDB Atlas
3. Procedural memory
Your system prompt, tool definitions, few-shot examples, fine-tuned weights — how the agent knows to behave. Most teams write this once and never touch it again. That's where quality quietly dies.
4. Episodic memory
Structured records of past sessions, not raw logs, but summarised, tagged experience the agent can actually learn from. The rarest layer. The highest leverage.
Examples: Mem0, Zep, custom pipelines on top of Redis or Postgres
Most production agents have layer two and nothing else. The ones that will win are designed with all four from the start.
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