### Answer For conversations, I recommend Retell AI based on your priorities: Best balance of intelligence and cost: - GPT-4.1 – Strong intelligence, reasonable latency [(1) ]() - GPT-4.1-mini – Good balance of speed and capability at lower cost Fastest/lowest latency: - GPT-4.1-nano – Fastest option at $0.004/min [(2) ]() Highest intelligence: - GPT-5 or GPT-5.1 – Most capable models [(1) ]() For speech-to-speech (real-time voice) : - gpt-4o-realtime at $0.50/min or gpt-4o-mini-realtime at $0.125/min [(2) ]() Quick comparison from the changelog: - Intelligence: GPT 4.1 > GPT 4o mini > GPT 4o > GPT 4.1 mini > GPT 4.1 nano - Latency (lower is faster) : GPT 4.1 nano < GPT 4.1 mini < GPT 4o mini < GPT 4o < GPT 4.1 For most use cases, GPT-4.1 or GPT-4.1-mini offer a solid starting point. If latency is critical, go with GPT-4.1-nano. For tool calling, a lower

model_temperature

is recommended. [(3) ]()

​ To learn more, see the sources I considered: [[1] List Retell LLMs](https://docs.retellai.com/api-references/list-retell-llms) [[2] Platform Changelogs | Retell AI](https://www.retellai.com/changelog) [[3] Create Retell LLM](https://docs.retellai.com/api-references/create-retell-llm) ​

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

### Answer Good question! While pricing may appear similar, the key reasons to choose different models come down to latency and **use case fit**: Latency differences matter for voice: - GPT-4.1-nano has the lowest latency, making conversations feel more natural with faster responses [(1) ]() - GPT-4.1-mini is faster than GPT-4.1 but slightly less intelligent - GPT-4.1 has higher latency but stronger reasoning Use case recommendations: - Function calling / data collection: Use temperature 0.0–0.3 for highly consistent, deterministic responses [(2) ]() - General customer service: Temperature 0.3–0.5 works well - Sales outreach: Temperature 0.5–0.7 for engaging but focused conversations Why faster models can be better: For voice AI, lower latency directly impacts user experience. Production voice agents typically aim for 800ms or lower latency to maintain conversational flow [(3) ]() . A faster model like GPT-4.1-nano may produce slightly less sophisticated responses, but the speed improvement can make conversations feel more natural. Bottom line: If your agent handles straightforward tasks (appointment booking, data collection) , a faster/cheaper model like GPT-4.1-nano or GPT-4.1-mini is often the better choice. Reserve GPT-4.1 or GPT-5 for complex reasoning tasks where intelligence matters more than speed.

​ To learn more, see the sources I considered: [[1] Platform Changelogs | Retell AI](https://www.retellai.com/changelog) [[2] Configure LLM Options](https://docs.retellai.com/build/llm-options) [[3] Performance-related configurations and noticeable latency during live calls](https://community.retellai.com/t/performance-related-configurations-and-noticeable-latency-during-live-calls/747) ​

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