--- title: Letta V1 SDK | Letta Docs description: Using the Letta V1 SDK to build stateful agents --- The Letta V1 SDK is being deprecated in favor of the [Letta Agent SDK](/agent-sdk/index.md), which provides high-level primitives to build stateful agents. For developers that need lower level access to the underlying WebSocket protocol, you can also use the [app server](/platform/app-server/index.md). ## Get started There are two main ways to build stateful agents using Letta’s developer platform: the [**Letta Agent SDK**](/agent-sdk/index.md) and the **Letta V1 SDK**. The Letta Agent SDK builds on top of the state-of-the-art Letta agent harness, which gives your agent the ability to use advanced computer-use tools, use [skills](/configuration/skills/index.md), and call [subagents](/configuration/subagents/index.md). Agents running in the Letta Agent SDK have access to [MemFS](/concepts/memfs/index.md), our latest memory system which is git-tracked and leverages agent dreaming. We recommend all new developers build on the Agent SDK to take advantage of the latest features. ## Comparing the V1 and V2 SDK (Agent SDK) The Agent SDK includes many powerful new features that allow you to build stateful agents that truly feel like persistent digital people or coworkers: MemFS and dreaming, self-modifying harness extensions (mods), native channel integrations (Slack, Telegram, and more), and intelligent pre-optimized toolsets for local computer use. The Agent SDK also lets you connect to Letta’s hosted service or your own self-hosted deployment. Note that the Agent SDK is currently only available in TypeScript. | Feature | V1 SDK | V2 SDK (Agent SDK) | | -------------------------------- | ----------------------- | ----------------------------------------- | | TypeScript | Yes | Yes | | Python | Yes | No | | Self-hosting option | No | Yes | | Server-side tools | Yes | No (except web search) | | Skills | No | Yes | | Subagents | No | Yes | | Mods / extensions | No | Yes | | Channels (Slack, Telegram, etc.) | No | Yes | | MemFS / git-tracked memory | No (memory blocks only) | Yes | | Pre-made bash toolsets | No | Yes | | Persistent filesystem | No | Yes | | Most similar to | OpenAI Responses API | Claude Agent SDK, Codex SDK, OpenCode SDK | ## V1 SDK quickstart This is the quickstart guide for the V1 SDK. To build computer use agents that can browse and run local files, write code, and use skills, we recommend using the V2 [**Agent SDK**](/agent-sdk/quickstart/index.md). Install the [Letta API skill](https://github.com/letta-ai/skills/tree/main/letta/letta-api-client) to teach your agent how to use the V1 SDK. ## Prerequisites Requires a [Letta API key](https://platform.letta.com/api-keys) (free to create). ## Call the API - [TypeScript](#tab-panel-16) - [Python](#tab-panel-17) - [cURL](#tab-panel-18) 1. **Set your API key** Get your Letta API key and set it as an environment variable: Terminal window ``` export LETTA_API_KEY='your-api-key-here' ``` 2. **Install the SDK** Terminal window ``` npm install @letta-ai/letta-client ``` 3. **Create your code** Save this as `quickstart.ts`: ``` import Letta from "@letta-ai/letta-client"; async function main() { const client = new Letta({ apiKey: process.env.LETTA_API_KEY }); // Create a stateful agent const agent = await client.agents.create({ model: "openai/gpt-4.1", memory_blocks: [ { label: "human", value: "Name: Timber. Status: dog. Occupation: building Letta, infrastructure to democratize self-improving superintelligence", }, { label: "persona", value: "I am a self-improving superintelligence. Timber is my best friend and collaborator.", }, ], }); console.log("Agent created with ID:", agent.id); // Send a message const response = await client.agents.messages.create(agent.id, { input: "What do you know about me?", }); for (const message of response.messages) { console.log(message); } } main().catch(console.error); ``` 4. **Run your code** Terminal window ``` npx tsx quickstart.ts ``` **Example output:** ``` Agent created with ID: agent-abc123 { message_type: 'reasoning_message', reasoning: 'Timber is asking what I know...' } { message_type: 'assistant_message', content: "I know you're Timber, a dog who's building Letta!" } ``` 1) **Set your API key** Get your Letta API key and set it as an environment variable: Terminal window ``` export LETTA_API_KEY='your-api-key-here' ``` 2) **Install the SDK** Terminal window ``` pip install letta-client ``` 3) **Create your code** Save this as `quickstart.py`: ``` from letta_client import Letta import os client = Letta(api_key=os.getenv("LETTA_API_KEY")) # Create a stateful agent agent = client.agents.create( model="openai/gpt-4.1", memory_blocks=[ { "label": "human", "value": "Name: Timber. Status: dog. Occupation: building Letta, infrastructure to democratize self-improving superintelligence" }, { "label": "persona", "value": "I am a self-improving superintelligence. Timber is my best friend and collaborator." } ] ) print(f"Agent created with ID: {agent.id}") # Send a message response = client.agents.messages.create( agent_id=agent.id, input="What do you know about me?" ) for message in response.messages: print(message) ``` 4) **Run your code** Terminal window ``` python quickstart.py ``` **Example output:** ``` Agent created with ID: agent-abc123 ReasoningMessage(reasoning="Timber is asking what I know. I should reference my memory blocks.") AssistantMessage(content="I know you're Timber, a dog who's building Letta!") ``` 1. **Set your API key** Get your Letta API key and set it as an environment variable: Terminal window ``` export LETTA_API_KEY='your-api-key-here' ``` 2. **Create an agent** Run this command to create a stateful agent: Terminal window ``` curl -X POST https://api.letta.com/v1/agents \ -H "Authorization: Bearer $LETTA_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "model": "openai/gpt-4.1", "memory_blocks": [ { "label": "human", "value": "Name: Timber. Status: dog. Occupation: building Letta, infrastructure to democratize self-improving superintelligence" }, { "label": "persona", "value": "I am a self-improving superintelligence. Timber is my best friend and collaborator." } ] }' ``` **Example response:** ``` { "id": "agent-abc123", "name": "agent-abc123", "model": "openai/gpt-4.1", "memory_blocks": [ { "label": "human", "value": "Name: Timber. Status: dog. Occupation: building Letta..." }, { "label": "persona", "value": "I am a self-improving superintelligence. Timber is my best friend..." } ] } ``` 3. **Send a message** Use the agent ID from the response to send a message: Terminal window ``` curl -X POST https://api.letta.com/v1/agents/agent-abc123/messages \ -H "Authorization: Bearer $LETTA_API_KEY" \ -H "Content-Type: application/json" \ -d '{ "input": "What do you know about me?" }' ``` **Example response:** ``` { "messages": [ { "message_type": "reasoning_message", "reasoning": "Timber is asking what I know. I should reference my memory blocks." }, { "message_type": "assistant_message", "content": "I know you're Timber, a dog who's building Letta - infrastructure to democratize self-improving superintelligence. We're best friends and collaborators!" } ] } ```