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Speech To Text - S0 - Error 429 on first call

Luca Proserpio 0 Reputation points
2025-04-22T22:14:43.52+00:00

Hi everyone,

I’m running into a strange issue with the Azure Speech-to-Text REST API. My workflow is:

  1. I call the endpoint: POST https://<my-resource>.cognitiveservices.azure.com/speechtotext/transcriptions:transcribe?api-version=2024-11-15 If I haven’t made any calls for a few hours, my very first request returns HTTP 429 Too Many Requests.
  2. After that 429 error, subsequent calls succeed normally until the next long idle period.

Questions:

Why does the very first call after an idle period return 429?

Is there an internal “warm‑up” or throttling behavior that I’m missing?

  1. How can I prevent this 429 on the first request without having to retry manually? Now i just set up a 3 tentative steps as fallback with a delay between, and often the second or third one is returning successfully the result.

Any insights or suggestions would be greatly appreciated. Thanks in advance!

Azure AI Speech
Azure AI Speech
An Azure service that integrates speech processing into apps and services.
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  1. Divyesh Govaerdhanan 3,205 Reputation points
    2025-04-23T02:30:33.8266667+00:00

    Hello,

    Welcome to Microsoft Q&A,

    The behavior you're experiencing an HTTP 429 "Too Many Requests" error on the first call to the Azure Speech-to-Text REST API after a period of inactivity is indicative of the service's autoscaling mechanism. Azure's Speech service dynamically allocates resources based on demand, and after a prolonged idle period, the service may need time to scale up resources to handle new requests.

    When the Speech service has been idle, it may not have sufficient resources immediately available to handle incoming requests. The first request after such an idle period can trigger the service to scale up its resources. During this scaling process, the service may temporarily reject requests, resulting in a 429 error.

    To mitigate this issue, consider the following strategies:

    1. Implement Retry Logic (As you have implemented currently)
    2. Periodic Warm-Up Requests - Send periodic light weight request to keep it active

    Please Upvote and Accept the answer if it helps!!

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