### Answer Based on the available sources, smaller models respond faster when it comes to LLM response time. [(1) ]() Model choice is often one of the largest factors in LLM response time, though the actual impact depends on your specific agent. Key points about model speed: - Smaller models respond faster, so if your use case can tolerate slightly less reasoning, switching to a smaller model noticeably reduces latency. - Larger, reasoning-oriented models are slower to first token—they trade latency for capability. - Latency also varies between providers for models of a similar size, so trying a comparable model from a different provider can help if you've already trimmed model size and prompt. The sources note that Retell AI achieved an average time-to-first-token of 180ms and end-to-end latency of 620ms in testing. [(2) ]() However, the specific model name with the absolute shortest response time isn't explicitly stated in the documentation. To identify which model works best for your use case, verify the actual LLM latency using the per-call latency breakdown before making changes, as not every agent is bottlenecked by the same factor. [(1) ]()

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

​ To learn more, see the sources I considered: [[1] Troubleshoot high latency](https://docs.retellai.com/reliability/troubleshoot-latency) [[2] ](https://www.retellai.com/resources/ai-voice-agent-latency-face-off-2025) ​

### Answer I don't have information in the available sources that explicitly names which specific LLM model has the absolute shortest response time. The sources mention that smaller models generally respond faster, and list available model options including gpt-4.1-nano, gpt-5-nano, gpt-5.4-nano, and others [(1) ]() [(2) ]() [(3) ]() , but they don't specify which one has the absolute shortest response time. For the fastest response, you'd typically want to test the smallest available models (like the "nano" variants) , but the actual performance depends on your specific use case and configuration.

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

​ To learn more, see the sources I considered: [[1] Get Retell LLM](https://docs.retellai.com/api-references/get-retell-llm) [[2] Create Retell LLM](https://docs.retellai.com/api-references/create-retell-llm) [[3] Update Retell LLM](https://docs.retellai.com/api-references/update-retell-llm) ​