Sonzai vs Letta
Short answer: Sonzai is a hosted memory and personality API — you call it from any backend and get state back. Letta (formerly MemGPT) is an agent framework with self-editing memory — you run an agent runtime that owns the loop. Choose Sonzai if you want a drop-in API for any LLM integration. Choose Letta if you want a full agent framework with its own runtime.
At a glance
| Feature | Sonzai | Letta |
|---|---|---|
| Type | Hosted API + SDKs | Open-source framework + cloud |
| Architecture | API you call from your backend | Agent runtime that owns the loop |
| Memory model | Hierarchical tree (facts, episodes, summaries) | Core memory + archival memory |
| Personality | Big Five (OCEAN) with trait evolution | — |
| Mood / emotion | 4D mood (valence, arousal, tension, affiliation) | — |
| Relationships | Yes | — |
| Self-editing memory | Via REST API | Yes (built-in) |
| MCP support | Native MCP server | Available |
| SDKs | TypeScript, Python, Go | Python |
| Best for | Drop-in state for any LLM app | Full agent framework |
When to choose Sonzai
- →You already have an LLM integration and want to add stateful memory without rewriting it.
- →You don't want to run or manage an agent runtime.
- →You need personality, mood, and relationships, not just memory.
- →You want SDKs in TypeScript, Python, and Go.
- →You're building production apps and want a managed service with SLAs.
When to choose Letta
- →You want a full agent framework that owns the control loop.
- →You want self-editing memory as a core architectural pattern (the MemGPT idea).
- →You're comfortable running an agent runtime in your stack or want the open-source option.
- →Your team is Python-first and your product is research- or experimentation-focused.
What makes Sonzai different
Letta is a framework — it gives you an opinionated agent loop with self-editing memory at its core. Sonzai is a service — it gives you state (memory, personality, mood, relationships) that you can call from any LLM integration. If you want to keep your existing LLM code and add long-term memory, personality, and emotional continuity in an afternoon, Sonzai fits that shape.
Sonzai also bundles things Letta doesn't: Big Five personality with trait evolution, a 4D mood model, relationship tracking, and a knowledge base with graph search.
FAQ
What is the difference between Sonzai and Letta?
Sonzai is a hosted API for state (memory, personality, mood, relationships). Letta is an agent framework with a self-editing memory runtime. Sonzai is drop-in; Letta is a full framework.
Is Sonzai a Letta alternative?
Yes — for developers who want stateful agents without managing an agent runtime.
Is Letta the same as MemGPT?
Letta is the productized version of the MemGPT research project, now offered as an open-source framework with a hosted cloud option.
Does Sonzai have self-editing memory?
Sonzai's memory is updated automatically through interactions and is editable via REST. It does not require an agent runtime that edits its own memory mid-loop.
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