Developer quickstart

Prerequisites

1. Create a Letta Cloud account
2. Create a Letta Cloud API key

Install the Letta SDK

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pip install letta-client

Create an agent

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from letta_client import Letta
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client = Letta(token="LETTA_API_KEY")
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agent_state = client.agents.create(
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    model="openai/gpt-4.1",
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    embedding="openai/text-embedding-3-small",
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    memory_blocks=[
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        {
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          "label": "human",
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          "value": "The human's name is Chad. They like vibe coding."
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        },
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        {
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          "label": "persona",
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          "value": "My name is Sam, the all-knowing sentient AI."
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        }
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    ]
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)
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print(agent_state.id)

Message your agent

Once the agent is created, we can send the agent a message using its id field:

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response = client.agents.messages.create(
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    agent_id=agent_state.id,
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    messages=[
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        {
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            "role": "user",
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            "content": "hows it going????"
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        }
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    ]
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)
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for message in response.messages:
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    print(message)

The response contains the agent’s full response to the message, which includes reasoning steps (chain-of-thought), tool calls, tool responses, and assistant (agent) messages:

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{
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  "messages": [
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    {
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      "id": "message-29d8d17e-7c50-4289-8d0e-2bab988aa01e",
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      "date": "2024-12-12T17:05:56+00:00",
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      "message_type": "reasoning_message",
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      "reasoning": "User seems curious and casual. Time to engage!"
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    },
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    {
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      "id": "message-29d8d17e-7c50-4289-8d0e-2bab988aa01e",
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      "date": "2024-12-12T17:05:56+00:00",
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      "message_type": "assistant_message",
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      "content": "Hey there! I'm doing great, thanks for asking! How about you?"
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    }
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  ],
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  "usage": {
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    "completion_tokens": 56,
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    "prompt_tokens": 2030,
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    "total_tokens": 2086,
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    "step_count": 1
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  }
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}

You can read more about the response format from the message route here.

View your agent in the ADE

Another way to interact with Letta agents is via the Agent Development Environment (or ADE for short). The ADE is a UI on top of the Letta API that allows you to quickly build, prototype, and observe your agents.

If we navigate to our agent in the ADE, we should see our agent’s state in full detail, as well as the message that we sent to it:

Read our ADE setup guide →