Letta (formerly MemGPT)

Letta provides two different SDK paths:

1. Agent SDK (Recommended): The modern TypeScript SDK (@letta-ai/letta-agent-sdk) designed for building stateful agents. It supports cloud, local, and self-hosted backends.
2. V1 SDKs (Legacy): These target the Letta API directly.
   • TypeScript: @letta-ai/letta-client
   • Python: letta-client

New projects should use the Agent SDK.

The extent of data collection depends on how you use Letta:

• Self-hosted / Local Backends: If you are running your own model backends, Letta does not collect data on your messages or prompts.
• Hosted Services (e.g., hosted endpoints, Discord Bot): Letta collects the data used to render these services, which includes message requests and message responses. This data may be used to improve services and train future models.

Letta triggers webhooks based on your execution architecture:

1. With Temporal (Recommended)

Webhooks are wrapped as Temporal activities (send_step_complete_webhook). This provides:

• Built-in retry logic and configurable timeouts (Start-to-close: 15s, Schedule-to-close: 30s).
• Full observability in the Temporal UI.
• Durability guarantees and activity history.

2. Without Temporal (Direct Execution)

Webhooks are called directly from the StepManager service methods (update_step_success_async, update_step_error_async, or update_step_cancelled_async) after the step status is committed to the database.

Critical Reliability Note

Webhook failures do not prevent step completion. The step is always marked as complete in the database before the webhook is attempted. If a webhook times out or returns an error, the agent execution continues uninterrupted.

By default, Letta applications collect basic anonymous telemetry data (such as clicks and crashes) to inform the product roadmap. To opt out of this collection, modify your configuration file to include the following setting:

telemetry_disabled = True

To establish a secure localhost HTTPS connection to the Agent Deployment Environment (ADE), you must use mkcert to generate valid local certificates. Follow these steps:

1. Install mkcert.
2. Run mkcert -install to set up the local Certificate Authority.
3. Start Letta with the environment variable LOCAL_HTTPS=true.
4. Open the Letta dashboard at https://app.letta.com/development-servers/local/dashboard.
5. Click "Add remote server" and use https://localhost:8283 as the URL. Leave the password blank unless you have explicitly secured your ADE with a password.

LOCAL_HTTPS=true letta run

The TS Server is a skeleton TypeScript application designed to support user-defined tool call functions. It is intended to run inside a Modal container. The architecture consists of three main components:

• server.ts: A Node process that listens on a Unix socket.
• entrypoint.ts: A lightweight function that deserializes JSON-encoded input strings into inputs for your user-defined function.
• user-function.ts: The file where you define your custom logic.

To set up and run the server locally, follow these steps:

npm install
npm run build
npm run start

Use the Letta Agent SDK (TypeScript) to integrate stateful agents into your applications. You can run agents on the Letta cloud (Constellation), locally on your machine, or against a self-hosted App Server.

npm install @letta-ai/letta-agent-sdk

You can receive webhook notifications whenever an agent step reaches a terminal state (SUCCESS, FAILED, or CANCELLED). To enable this, set the following environment variables in your Letta environment:

Required

• STEP_COMPLETE_WEBHOOK: The full URL endpoint that will receive the POST requests.

Optional

• STEP_COMPLETE_KEY: A secret string used for authentication. If provided, Letta will include it in the Authorization header as Bearer {key}.

Usage Example

export STEP_COMPLETE_WEBHOOK="https://your-app.com/api/webhooks/step-complete"
export STEP_COMPLETE_KEY="your-secret-webhook-key-12345"

# Start your Letta server
python -m letta.server

To test your webhook integration:

1. Use a service like webhook.site to generate a unique URL.
2. Set STEP_COMPLETE_WEBHOOK to that URL.
3. Set a STEP_COMPLETE_KEY for testing.
4. Run your tests or an agent to trigger completions.

# Example using webhook.site
export STEP_COMPLETE_WEBHOOK="https://webhook.site/your-unique-url"
export STEP_COMPLETE_KEY="test-key-123"

# Run tests
python -m pytest apps/core/letta/services/webhook_service_test.py -v

Depending on your location (e.g., GDPR in the EU or specific US state laws like California), you may have rights regarding your personal data, including:

• Requesting access to, correction of, or deletion of your data.
• Objecting to or limiting the processing of your data.
• Requesting data portability.
• Opting out of the sale or sharing of personal information.

To exercise these rights, contact Letta via email at contact@charlespacker.com. You will be required to verify your identity (e.g., by contacting from the email address associated with your account) before any data is disclosed or deleted.

To run agents locally in your terminal with advanced memory, skills, and subagents, use the Letta Code CLI. This requires Node.js 22.19+.

1. Install the CLI globally via npm: npm install -g @letta-ai/letta-code
2. Launch an agent by running: letta in your terminal.