Using the API

API Overview

Introduction to the Letta API including REST endpoints and authentication.

The Letta API is a RESTful API at https://api.letta.com that provides programmatic access to stateful agents with persistent memory.

Prerequisites

To use the Letta API, you’ll need an API key.

For step-by-step setup instructions, see the quickstart.

Authentication

All requests to the Letta API must include these headers:

Header	Value	Required
`Authorization`	`Bearer <your-api-key>`	Yes
`Content-Type`	`application/json`	Yes

If you are using the Client SDKs, the SDK will send these headers automatically.

Client SDKs

Letta provides official SDKs for Python and TypeScript that simplify API integration, providing:

Automatic header management
Type-safe request and response handling
Built-in retry logic and error handling

Python

pip install letta-client

from letta_client import Letta

client = Letta(api_key="your-api-key")

agent = client.agents.create(
    model="openai/gpt-4.1",
)

response = client.agents.messages.create(
    agent_id=agent.id,
    input="Hello!"
)

TypeScript

npm install @letta-ai/letta-client

import Letta from "@letta-ai/letta-client";

const client = new Letta({ apiKey: "your-api-key" });

const agent = await client.agents.create({
  model: "openai/gpt-4.1",
});

const response = await client.agents.messages.create(agent.id, {
  input: "Hello!",
});

Next steps

Quickstart Prerequisites, step-by-step tutorial, and examples.

Core concepts Understand agents, memory blocks, and tools.