### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

I am trying to use `openai/whisper-1` for audio transcription via the OpenRouter provider. Although the model is configured in the LiteLLM proxy, the request fails with a provider mapping error and a 400 Bad Request.

### Questions & Context: I have reviewed the documentation (https://docs.litellm.ai/docs/audio_transcription) but I'm still facing issues.

1. Is `openai/whisper-1` currently unsupported when using the OpenRouter provider in LiteLLM? 2. If it's not supported, what is the recommended configuration or workaround to perform audio transcription through LiteLLM with OpenRouter?

**Expected Behavior:** Successful audio transcription using Whisper-compatible models through OpenRouter.

**Actual Behavior:** I receive a `ValueError: Unmapped provider` and an OpenAI BadRequestError indicating an invalid model name.

### Steps to Reproduce

1. Add `openai/whisper-1` to LiteLLM models via the Admin UI/config. 2. Set the provider to `openrouter`. 3. Make an audio transcription request (e.g., using the `/v1/audio/transcriptions` endpoint). 4. S…