# April 29, 2026

## LLM Model Updates & Cartesia Speed Control

### GPT-5.5 LLM Model Support

OpenAI's GPT-5.5 model is now available as a managed LLM in the Voice Agent API. GPT-5.5 is an Advanced tier model.

Set the model in your agent configuration:

```json
{
  "agent": {
    "think": {
      "provider": {
        "type": "open_ai",
        "model": "gpt-5.5",
        "temperature": 0.7
      }
    }
  }
}
```

For the full list of supported models and pricing tiers, see the [Voice Agent LLM Models documentation](/guides/self-hosted-deployments-3-voice-agent-llm-models).

### Llama Nemotron Super 49B Removed

The `llama-nemotron-super-49B` (Llama Nemotron Super 49B) model has been removed from the NVIDIA provider due to poor performance. The `nemotron-3-nano-30B-A3B` model remains available. See the [NVIDIA models table](/guides/self-hosted-deployments-3-voice-agent-llm-models#nvidia) for current options.

### Cartesia TTS Speed Control

The `agent.speak.provider.speed` parameter now supports Cartesia TTS in addition to Deepgram TTS. For Cartesia, the parameter accepts the following preset values:

- `slowest`
- `slow`
- `normal`
- `fast`
- `fastest`

You can also pass a numerical value for more granular control. See the [Cartesia speed documentation](https://docs.cartesia.ai/build-with-cartesia/capability-guides/volume-speed-emotion) for details.

```json
{
  "agent": {
    "speak": {
      "provider": {
        "type": "cartesia",
        "model_id": "sonic-2",
        "voice": {
          "mode": "id",
          "id": "a167e0f3-df7e-4d52-a9c3-f949145efdab"
        },
        "speed": "fast"
      }
    }
  }
}
```

For more details, see the [TTS Models documentation](/guides/self-hosted-deployments-3-voice-agent-tts-models#deepgram-managed-cartesia-tts-models).

## Related pages

- [Amazon SageMaker](./amazon-sagemaker-index.md)
- [Aura](./aura-index.md)
- [Changelog](../changelog.md)
- [Custom Vocabulary](./custom-vocabulary-index.md)
- [Deepgram's Docs](../index.md)
- [Deployment](./deployment-index.md)
- [Docker/Podman](./docker-podman-index.md)
- [Features](./features-index.md)
- [Flux TTS](./flux-tts-index.md)
- [Formatting](./formatting-index.md)

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