Letta Python Client

1.10.3 verified Fri May 01 auth: no python

The official Python library for the Letta API, providing a typed interface to agents, conversations, messages, tools, and more. Current version 1.10.3, requires Python >=3.9, actively maintained with frequent releases (multiple per month).

pip install letta-client

Common errors

error ModuleNotFoundError: No module named 'letta' ↓

cause Typo in package name: installed `letta-client` but imported as `letta`.

fix

Install with pip install letta-client then import with from letta import Letta.

error ImportError: cannot import name 'Letta' from 'letta' ↓

cause Outdated version or incorrect import path. The SDK was previously structured differently.

fix

Upgrade to latest: pip install --upgrade letta-client and use from letta import Letta.

error letta.APIConnectionError: Connection error ↓

cause Missing or invalid API key. The client cannot reach the Letta API.

fix

Set the LETTA_API_KEY environment variable or pass api_key to the Letta constructor.

Warnings

breaking The client constructor changed from positional to keyword-only arguments in v1.x. Use `Letta(api_key=...)` instead of `Letta('...')`. ↓

fix Use keyword arguments: `Letta(api_key='...')`. For environment variable, omit api_key entirely.

gotcha Methods that accept `model` or `model_id` may be case-sensitive. Use exact model identifiers from the Letta dashboard. ↓

fix Always use the exact model string as returned by `client.models.list()`.

gotcha Streaming responses require `stream=True` parameter in message creation endpoints. Without it, the response is non-streaming and may hang if large. ↓

fix Add `stream=True` to create calls: `client.messages.create(..., stream=True)`.

Imports

Letta
wrong
```
import letta
```
correct
```
from letta import Letta
```
Direct module import does not expose the client; use named import.

Quickstart

Initialize the Letta client and list all agents.

import os
from letta import Letta

client = Letta(api_key=os.environ.get('LETTA_API_KEY', ''))
agents = client.agents.list()
print(agents)