Letta vs 
Pydantic AI
Letta vs Pydantic AI compared for 2026 — features, license, ease of use, performance and which one to choose. Stateful agents with long-term memory vs Type-safe agents for production.
Updated regularly · curated by OpenSourceAI.tech
Letta vs Pydantic AI at a glance
| Spec | Letta | Pydantic AI |
|---|---|---|
| Category | AI agent framework | AI agent framework |
| Type | Agent runtime (memory) | Agent framework (typed) |
| License | Apache-2.0 | MIT |
| Runs locally | Self-hosted | Cloud-optional |
| Primary language | Python | Python |
| Ease of use | Advanced | Intermediate |
| Best for | agents that remember across sessions | production agents with typed outputs |
| GitHub stars | 24k | 18.9k |
How Letta and Pydantic AI score
| Criterion | Letta | Pydantic AI |
|---|---|---|
| Popularity | 3.5 | 3.5 |
| Maintenance | 5.0 | 5.0 |
| Ease of use | 2.5 | 3.5 |
| Privacy | 4.5 | 3.5 |
| License freedom | 5.0 | 5.0 |
Scores are computed automatically from public signals — GitHub stars (popularity), recent commit activity (maintenance), license type (freedom), local-first design (privacy) and onboarding complexity (ease of use). Indicative, not a verdict.
What each one is
Letta
Letta (formerly MemGPT) is a framework and server for building stateful agents with long-term memory that persists across sessions, with a visual agent editor.
- Persistent long-term agent memory
- Server with REST API and visual editor
- Model-agnostic and self-hostable
Pydantic AI
Pydantic AI brings the ergonomics and type-safety of Pydantic to agent development, with structured outputs, dependency injection and model-agnostic support.
- Type-safe, structured agent outputs
- Familiar Pydantic developer experience
- Model-agnostic with great tooling
Key differences
Letta is agent runtime (memory), while Pydantic AI is agent framework (typed). Their licenses differ (Apache-2.0 vs MIT), which matters if you ship a commercial product. Letta leans more advanced-friendly, whereas Pydantic AI is more suited to intermediate users. They also differ in how they run (Self-hosted vs Cloud-optional). In short, Letta fits agents that remember across sessions, and Pydantic AI fits production agents with typed outputs.
Which should you choose?
Choose Letta for agents that remember across sessions. Choose Pydantic AI for production agents with typed outputs.
There is rarely one winner — many setups use both. The right pick depends on your hardware, your team's skills, and whether you value simplicity or control.
Frequently asked questions
Is Letta or Pydantic AI easier to use?
Pydantic AI is generally the easier of the two to get started with, while Letta rewards more setup with more control.
Are Letta and Pydantic AI free?
Letta is free and open source (Apache-2.0), and Pydantic AI is free and open source (MIT). Neither charges for the core software.
Can I run Letta and Pydantic AI locally?
Letta: self-hosted · Pydantic AI: cloud-optional. Both can be used without sending your data to a third-party cloud where their setup allows.
Letta vs Pydantic AI — which should I pick in 2026?
Choose Letta for agents that remember across sessions. Choose Pydantic AI for production agents with typed outputs.
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