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Let users subscribe to notifications for long-running agent tasks instead of waiting. With Restate’s durable promises, you can coordinate between agent execution and notification handlers, no extra infrastructure needed.

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How does Restate help?

Building this yourself requires message queues, databases, and polling workers. Restate replaces all that with a few lines of code:
  • Durable promises: Create promises that survive failures and restarts
  • Zero infrastructure: No queues, databases, or polling workers needed
  • No race conditions: Late subscribers immediately receive already-resolved results
  • Serverless-friendly: Handlers suspend while waiting - pay only for active compute
  • Works with any LLM SDK and any language supported by Restate

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Example

The pattern works in two steps: Step 1: The agent handler processes the request and resolves a durable promise with the result. Step 2: The notification handler awaits that promise and sends the notification when it resolves.
Python
agent_service = restate.Workflow("AsyncNotificationsAgent")

agent = Agent(
    name="Assistant",
    instructions="You are a helpful assistant.",
)


@agent_service.main()
async def run(ctx: restate.WorkflowContext, user_query: str):
    # Process the user's query with the AI agent
    response = await DurableRunner.run(agent, user_query)

    # Notify other handlers of the response
    await ctx.promise("agent_response").resolve(response.final_output)

    # Return synchronous response
    return response.final_output


@agent_service.handler()
async def on_notify(ctx: restate.WorkflowContext, email: str):
    # Wait for the agent's response
    response = await ctx.promise("agent_response", type_hint=str).value()

    # Send the email
    await ctx.run_typed("Email", send_email, email=email, body=response)
View on GitHub: Python Check out the SDK documentation for more details on the durable promises API (TS / Python).
This pattern is implementable with any of our SDKs and any AI SDK. If you need help with a specific SDK, please reach out to us via Discord or Slack.
1

Requirements

  • AI SDK of your choice (e.g., OpenAI, LangChain, Pydantic AI, LiteLLM, etc.) to make LLM calls.
  • API key for your model provider.
2

Download the example

Python
git clone https://github.com/restatedev/ai-examples.git &&
cd ai-examples/openai-agents/examples
3

Start the Restate Server

restate-server
4

Start the Service

Export the API key of your model provider as an environment variable and then start the agent. For example, for OpenAI:
Python
export OPENAI_API_KEY=your_openai_api_key
uv run .
5

Register the services

Service Registration
6

Send a request

In the UI (http://localhost:9070), click on the run handler of the AsyncNotificationsAgent to open the playground and send a request to the run handler and then the on_notify handler.Or send requests via the terminal.First, start the agent asynchronously by adding /send to the end of the URL:
curl localhost:8080/AsyncNotificationsAgent/msg-123/run/send \
  --json '"Write a 1000-word description of Durable Execution"'
Then, asynchronously call the on_notify handler to send the agent response via email once it’s ready:
curl localhost:8080/AsyncNotificationsAgent/msg-123/on_notify/send \
  --json '"[email protected]"'
Notice that the key msg-123 is identical for both requests, to send them to the same workflow instance.
7

Check the Restate UI

In the Restate UI, you see how the notify handler waited on the agent response and then sent the email.