Demo open-source UI, built using the Letta Agent SDK

An example desktop application for running Letta agents with a visual interface.

What is the Letta OSS UI?

This repo contains an example desktop application for running Letta agents with a visual interface. The code is a fork of Claude-Cowork that replaces the Claude SDK with the @letta-ai/letta-agent-sdk. It provides a native desktop GUI for interacting with Letta agents.

Screen.Recording.2026-02-02.at.6.01.40.PM.mov

Why Letta Agent SDK?

The Letta Agent SDK is the SDK interface to Letta Code. Build agents with persistent memory that learn over time.

import { createAgent, resumeSession } from '@letta-ai/letta-agent-sdk';

// First session - agent learns something
const agentId = await createAgent();
const session1 = resumeSession(agentId);
await session1.send('Remember: the secret word is "banana"');
for await (const msg of session1.stream()) { /* ... */ }
session1.close();

// Later... agent still remembers
await using session2 = resumeSession(agentId);
await session2.send('What is the secret word?');
for await (const msg of session2.stream()) {
  if (msg.type === 'assistant') console.log(msg.content); // "banana"
}

Key concepts:

• Agent (agentId): Persistent entity with memory that survives across sessions
• Conversation (conversationId): A message thread within an agent
• Session (sessionId): A single execution/connection

Agents remember across conversations (via memory blocks), but each conversation has its own message history. This means you can run multiple concurrent conversations with the same agent - each conversation has its own message history while sharing the agent's persistent memory.

Quick Start

Prerequisites

• Bun or Node.js 22+
• For cloud mode: a Letta API key from app.letta.com/settings

Environment Setup

1. Copy .env.example to .env:

   cp .env.example .env

2. Pick a backend in .env (see .env.example for all options):

   Letta Cloud (agents stored in the cloud, tools run on your machine):

   LETTA_BACKEND=cloud
   LETTA_API_KEY=your-api-key-here

   Fully local runtime (agents stored on your machine, no API key):

   LETTA_BACKEND=local

   Self-hosted app server (see self-hosting docs):

   # In another terminal: letta server --backend local --listen ws://127.0.0.1:4500
   LETTA_BACKEND=remote
   LETTA_SERVER_URL=ws://127.0.0.1:4500

   If LETTA_BACKEND is unset, the app uses cloud when LETTA_API_KEY is set and local otherwise.

Running the App

# Clone the repository
git clone https://github.com/letta-ai/letta-cowork.git
cd letta-cowork

# Install dependencies
bun install

# Run in development mode
bun run dev

Architecture

The OSS UI uses @letta-ai/letta-agent-sdk to run agents.

How It Works

1. The app talks to a Letta app server through the SDK:
   • local / cloud backends: the SDK spawns and manages a bundled local app server (@letta-ai/letta-code)
   • remote backend: the SDK connects to your self-hosted app server over WebSocket
2. Each task resumes the app's agent (created on first run) as a new SDK session
3. Agent memory persists across conversations via memory blocks

Development

# Start development server (hot reload)
bun run dev

# Type checking
bun run build