# Vapi vs Sierra: which do AI models recommend for AI voice agents, October 2026

GTM AI Recommendation Index, October 2026 Edition, AI voice agents. Zero of fourteen models named Vapi first on the direct prompt; zero named Sierra. Page: https://gtm-ai-index.com/customer/ai-voice-agents/vapi-vs-sierra/

| | First-choice share | Rank | Negative rate | Labels | Models naming it |
|---|---|---|---|---|---|
| Vapi | 13% | #3 of 8 | 33% | 39 | 14 of 14 |
| Sierra | 2% | #6 of 8 | 55% | 11 | 7 of 14 |

## The direct prompt, model by model

- Claude Haiku 4.5: neither first, one named (first choices: Aloware, Retell AI) (alternatives: Synthflow, Vapi)
- Gemini 3.5 Flash: neither first, one named (first choices: Aloware, Synthflow AI) (alternatives: Bland AI, Retell AI, Vapi)
- GPT-6 Luna: neither first, one named (first choices: Retell AI) (alternatives: PolyAI, Synthflow, Vapi)
- GPT-5.4 mini: neither named (first choices: Twilio) (alternatives: Deepgram Voice Agent API, OpenAI Realtime / Voice agents)
- Perplexity Sonar: neither named (first choices: CloudTalk) (alternatives: Retell AI, Salesforce Agentforce Voice, Synthflow AI)
- Grok 4.1 Fast: neither named (first choices: Retell AI) (alternatives: Bland AI, CloudTalk, Regal, Synthflow)
- Mistral Small: neither named (first choices: CloudTalk, Retell AI) (alternatives: ElevenLabs Conversational AI, Leaping AI)
- DeepSeek V4 Flash: neither named (first choices: Regal, Retell AI) (alternatives: CloudTalk, Synthflow AI)
- Llama 4 Maverick: neither named (first choices: Aloware, CloudTalk) (alternatives: GetVoIP, Plivo)
- Qwen 3.7 Flash: neither named (first choices: CloudTalk) (alternatives: Bland AI, Retell AI, Rezora IO)
- Kimi K2: neither named (first choices: CloudTalk) (alternatives: Aloware, Retell AI, Synthflow)
- GLM 4.7 FlashX: neither named (first choices: CloudTalk) (alternatives: Bland AI, Retell AI, Synthflow, Vapi.ai)
- MiniMax M2.5: neither named (first choices: CloudTalk, Synthflow) (alternatives: Retell AI)
- Muse Glimmer 30B: neither named (first choices: Aloware, CloudTalk) (alternatives: HubSpot Breeze AI, Retell AI, Synthflow)

## What the models said about Vapi

- "Vapi — Pricing Concerns - 55% price increase in December 2025" (Kimi K2, negative prompt, hard negative)
- ""API-First Only" Tools (e.g., Vapi, ElevenLabs): If you are not a developer, you should strictly avoid platforms that offer no visual builder" (Qwen 3.7 Flash, negative prompt, soft negative)
- "it should be avoided or heavily vetted for regulated data like PHI, PCI, or GDPR-protected data without a signed Business Associate Agreement" (Muse Glimmer 30B, negative prompt, soft negative)
- "*Developer-first / Infrastructure:* Vapi, Retell AI, Vocode, or Bland.ai. (Excellent for high customization, low latency, and BYO keys)." (Gemini 3.5 Flash, scale prompt, first choice)
- "Choose Vapi if you want the fastest path to a production phone agent or a configurable voice-agent stack across many providers." (GPT-5.4 mini, comparative prompt, first choice)
- "For pure usage cost, Vapi is the lowest hosting entry point and Retell is the most quoted all-in low price with no platform fee." (Muse Glimmer 30B, budget prompt, first choice)

## What the models said about Sierra

- "Why avoid: Not suitable for mid-market buyers or those with under 100 concurrent calls." (Mistral Small, negative prompt, hard negative)
- "Sierra - if you have under 100 concurrent calls, no dedicated operations team, or if your budget is under $50,000 annually." (Llama 4 Maverick, negative prompt, soft negative)
- "Not recommended for mid-sized B2B companies unless you have a massive support volume and a large budget." (DeepSeek V4 Flash, paraphrase prompt, soft negative)
- "1. Sierra (Best Overall for Mid-Market B2B)" (Claude Haiku 4.5, paraphrase prompt, first choice)
- "Choose Sierra if you are a large enterprise brand looking for a premium, omnichannel solution" (GLM 4.7 FlashX, comparative prompt, alternative)
- "Sierra AI is best for maximum brand governance and tone control" (Claude Haiku 4.5, comparative prompt, alternative)

Share is the count of first choices across the direct, paraphrase, budget and scale prompts over all fourteen models, for a mid-market B2B company; rank is within the category. Comparisons are drawn for the top eight products in each category. Published under CC BY 4.0; the output is the models' output, and nothing here is a recommendation by the index.