Agent Memory Patterns

About this vault

Context windows are not memory. Every serious agent built after 2023 has had to answer the same question: where does the state go when the conversation ends? This vault tracks the four schools that emerged. The hierarchical school started with Charles Packer's MemGPT paper (Berkeley, October 2023), which framed the LLM as an operating system paging memory between tiers of storage. The MemGPT authors spun out Letta, which now ships memory blocks as an API, sleep-time compute as a second agent that rewrites state during idle windows, and a production agent server. The graph school is led by Zep: Graphiti (August 2024) is a temporal knowledge graph that beat MemGPT on the Deep Memory Retrieval benchmark and tracks how facts change over time. The episodic school comes from Stanford's Generative Agents (Park et al., 2023), whose memory stream of observations, reflections, and plans became the template for persistent characters. The hybrid school is everywhere else — Mem0, Cognee, MemOS stitching vector + graph + key-value into single pipelines. Meanwhile LangChain shipped LangMem, Anthropic released a memory tool in Claude Sonnet 4.5, OpenAI added ChatGPT memory at consumer scale, Cloudflare launched Agent Memory. Harrison Chase then argued the real point in April 2026: whoever owns your agent's harness owns your memory. Karpathy's LLM Wiki reframed the whole thing as an IDE-for-knowledge problem. This list picks the pieces that set the terms of the debate, not the ones that summarize it.