When the custom speech-to-text model expires, the real-time endpoint will automatically fall back to using the most recent base model for that locale.
Because of this automated fallback design, your agent's real-time speech recognition streams will not fail or throw a connection error. However, you will likely experience a drop in transcription accuracy, as the fallback base model lacks the domain-specific vocabulary, acronyms, or unique audio adaptations built into your custom model.
Immediate Impact Summary
Real-Time Endpoints: Continue to process requests. The endpoint swaps the expired custom model for the newest standard base model behind the scenes.
Batch Transcriptions (If used): Any batch transcription jobs explicitly targeting the expired custom model ID will fail with a 4xx error code.
Customization Loss: Specific jargon, formatting rules, or accents trained into your model will temporarily stop applying to incoming agent audio.
Reference:
https://learn.microsoft.com/en-us/azure/ai-services/speech-service/how-to-custom-speech-model-and-endpoint-lifecycle