Letta Agent SDK overview

The Letta Agent SDK is the SDK for stateful agents: create an agent once, then resume it from anywhere. Each agent has its own identity and long-term memory, and keeps both across conversations, models, and the computers it runs on.

That makes the agent — not the process, the session, or the machine — the durable object in your application. Most of the time you are reconnecting to an agent that already exists and already knows something, rather than creating a disposable one. Use the SDK to build multi-agent and multi-user applications, orchestrate agents dynamically, or put a custom interface on top of a Letta agent.

import { LettaAgentClient } from "@letta-ai/letta-agent-sdk";

const client = new LettaAgentClient({ backend: "cloud" });

// Create the agent once...
const agentId = await client.createAgent({
  persona: "You are Nora, a research analyst who tracks our competitors.",
});

// ...then resume it, from anywhere, for as long as it lives.
await using session = client.resumeSession(agentId);

await session.send("What changed since last week?");
for await (const message of session.stream()) {
  if (message.type === "assistant") process.stdout.write(message.content);
}

Start in order

1. Quickstart: install the SDK, create an agent, and stream its first response
2. Sessions, turns, and durability: the agent, conversation, and session model that the rest of these docs assume
3. Creating agents and Sending messages: configure memory and handle the event stream

What you need

• A JavaScript or TypeScript project
• A Letta API key for the cloud backend; the local backend needs no account
• Node.js 22.19+ only if you run the agent runtime yourself — the local backend, or a self-hosted App Server

Choose your next step

Start with the Quickstart when you are new to the SDK. Read Deployment when you need to decide where agent state lives and where tools execute — the SDK is model agnostic and reaches managed, local, and self-hosted deployments through one interface. Explore the demo apps for a React chat frontend, a mobile client, or an integration inside an existing desktop application. Browse Examples for smaller applications focused on individual SDK features. The source is on GitHub.