Changelog

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:

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

For the full list of supported models and pricing tiers, see the Voice Agent LLM Models documentation.

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 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 for details.

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

For more details, see the TTS Models documentation.