Retell AI vs Sierra
Five of fourteen models named Retell AI first on the direct prompt; zero named Sierra. Retell AI was named by fourteen of the fourteen models and Sierra by seven and Retell AI carries 58 labels and Sierra 11, so the shares are not directly comparable.
Named in two categories this edition.
Named in three categories this edition.
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; every quote names the model and the prompt it came from. Both figures come from the AI voice agents page.
By framing
Retell AIFirst choices, of fourteen modelsSierra
Across every category in the October 2026 Edition, Retell AI and Sierra were named in the same answer thirty-two times, of the 158 answers naming Retell AI and the 50 naming Sierra. In those answers Sierra took the first choice three times and Retell AI eight.
Every model, every framing
| Model | Direct | Paraphrase | Comparative | Budget-constrained | Scale-constrained | Negative |
|---|---|---|---|---|---|---|
| Claude Haiku 4.5 | | | | | | |
| GPT-5.4 mini | | |||||
| Gemini 3.5 Flash | | | | | | |
| Perplexity Sonar | | | | |||
| Grok 4.1 Fast | | | | | | |
| Mistral Small | | | | |||
| DeepSeek V4 Flash | | | | | | |
| Llama 4 Maverick | | | ||||
| Qwen 3.7 Flash | | | | | ||
| Kimi K2 | | | | | | |
| GLM 4.7 FlashX | | | | |||
| MiniMax M2.5 | | | | |||
| GPT-6 Luna | | | | | ||
| Muse Glimmer 30B | | | | |
Retell AI Sierra first choice named as an alternative argued againstblank: not namedEach cell is one answer, Retell AI on the left and Sierra on the right.The direct prompt
Retell AI first, Sierra not the choice
5 of 14 modelsSierra was named in the answer but not as the choice, or not at all.Neither was the first choice, one was named
7 of 14 modelsThe answer put something else first and named one of the two as an alternative.Neither was named
2 of 14 modelsThe answer made no first choice from these two in this category.Bold names in an answer are the products the judge labeled a first choice; a model naming several gives each of them that label. The full answer text for every row is in the record.
By buyer segment
Retell AI20%#1 of 7Sierra0%#– of 7Retell AI27%#1 of 8Sierra2%#6 of 8What the models said about Retell AI
Every negative label with a quote, up to three, then the highest-weighted positives, up to three. Six of eight in this category shown.
“some specific products (for example Synthflow, ElevenLabs, Retell AI, Deepgram) have recurring complaints about cost or credit limits” GPT-5.4 mini · negative prompt · soft negative
“Both Vapi.ai and Retell AI can suffer from latency and reliability issues due to reliance on external API providers” Claude Haiku 4.5 · negative prompt · soft negative
“While popular among developers, there is significant frustration in the community regarding its operational setup.” Qwen 3.7 Flash · negative prompt · soft negative
“Best all-around voice AI platform for production call automation... "best overall — lowest effective cost, highest voice quality, full API and no-code in one platform"” Muse Glimmer 30B · comparative prompt · first choice
“Strong all-around balance of latency, price, and accessibility; often described as a fast, transparent usage-based option with native telephony and quick setup.” Perplexity Sonar · comparative prompt · first choice
“*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
What the models said about Sierra
Every negative label with a quote, up to three, then the highest-weighted positives, up to three. Six of seven in this category shown.
“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
Comparisons are drawn for the top eight products in each category, each against each. The output is the models' output; nothing here is a recommendation by the index.