Comparison
PersistMemory vs LangChain memory
LangChain's memory classes manage what fits in a prompt. PersistMemory is a store that outlives the process. They solve adjacent problems and are frequently used together.
What LangChain memory is good at
LangChain's memory classes are context management, and they are good at it. Buffers, windows, summaries and entity memory all answer the same practical question: this conversation is longer than the model's context, so what goes in the prompt this turn? That question is real and it does not go away.
Where they actually differ
The two are not alternatives so much as different layers. LangChain memory lives inside a run and mostly inside a process; when the run ends, what survives is whatever you arranged to persist. PersistMemory is the thing you persist into, and it is queried rather than replayed: you ask what is known about a topic and get the handful of memories that answer, with their sources, instead of a summary of everything said so far.
| PersistMemory | LangChain memory | |
|---|---|---|
| Lifetime | Indefinite, across every application and assistant on the account. | The run, unless backed by a store you configure. |
| How recall works | A query returns ranked memories with sources and timestamps. | History is replayed or summarised into the prompt. |
| Sources beyond the chat | Connectors for mail, Drive, Slack, Teams, meetings and uploads. | Loaders exist for documents; wiring them into memory is yours to build. |
| Cost as history grows | Flat. Retrieval returns a few memories regardless of how much is stored. | Grows with the buffer, which is what summarisation exists to bound. |
| Using both | Common. LangChain manages the turn, PersistMemory answers what happened before it. | Same, from the other side. |
Pick LangChain memory when
- You need to fit a long conversation into a context window right now.
- The agent is short-lived and nothing needs to survive it.
- You are already deep in LangChain and want to stay in one abstraction.
Pick this when
- You want next month's conversation to know what this one decided.
- Several applications should share one memory rather than each keeping their own.
- You need to answer where a remembered fact came from.