Letta (formerly MemGPT) is a framework for building AI agents with advanced, persistent memory that learn and self-improve over time. It comes in two main forms: Letta Agent, a memory-equipped agent you run locally in the terminal, through a desktop app, or via channels like Slack, and the Letta Agent SDK (TypeScript), for embedding stateful agents into your own applications. Agents created with the SDK can run on Letta's hosted agent cloud (Constellation), fully locally on your machine, or against a self-hosted App Server. Agents are defined with a persona and knowledge about their human counterpart, hold long-running sessions, and stream responses back to the caller.
The CLI agent (Letta Code) supports skills and subagents and bundles pre-built ones for advanced memory and continual learning; it is model-agnostic, working across providers such as Anthropic and OpenAI. Note that this particular repository holds the legacy Letta server — the API server behind the V1 API and SDKs — and active development has moved to the Letta Agent repo, with self-hosting now done via the App Server. The previous-generation V1 client SDKs (TypeScript and Python) remain available, but the Agent SDK is the recommended path for new projects.