The Decision In One Sentence
Pick Letta if memory should shape how the agent behaves over time as part of the platform model. Pick Zep if memory should behave more like production infrastructure that feeds an existing application stack.
The Real Difference Is Where Memory Lives In The Design
Both tools sit in the memory layer, but they make different assumptions about the role memory should play. Letta pulls the design toward memory-first stateful agents. Zep pulls it toward managed context and production memory services that support a broader stack.
That is why the better choice usually appears once the team decides whether memory is supposed to define the system or support it.
When Letta Wins
- memory continuity is part of the product identity
- local development, self-hosting, or broader deployment flexibility matter
- stateful behavior over time should shape the agent platform itself
- the team wants more platform control around memory design
When Zep Wins
- the surrounding stack is already taking shape
- the team mainly needs production memory and context retrieval
- reducing internal engineering work around memory matters
- managed infrastructure is more attractive than deeper platform control
The Better Evaluation Path
Do not compare these tools on abstract "memory" language. Compare them on the role memory plays in your actual system.
- If memory is supposed to shape long-term agent behavior, start with Letta.
- If memory is supposed to feed personalization, retrieval, and production context into an existing stack, start with Zep.
- Keep the option whose memory model still makes sense once the rest of the application is in place.
When Neither Is The Best Next Page
If the real need is graph-based temporal memory, Graphiti may be the better next evaluation. If the real need is a thinner dedicated memory layer, Mem0 may be more relevant.
Bottom Line
Choose Letta when memory should sit at the center of the agent platform. Choose Zep when memory should behave more like managed production infrastructure serving the rest of the stack.