Retell.ai vs Sierra AI Comparison (2025)

Retell.ai
Starting at $0.07 – 0.08 /min
Retell AI offers fast, scalable voice agents with response times under a second and impressive developer flexibility. You can bring your own LLM, customize behavior deeply, and monitor everything through real-time dashboards. It’s well-suited for teams with in-house engineering that want control and scale. But the learning curve is real—getting up and running takes work, integrations often require custom scripts, and pricing isn’t transparent. While it performs well under the hood, Retell isn’t the most approachable platform for teams seeking simplicity or industry-ready templates out of the box.
Key Metrics
Latency
950 ms
Automation
55%
Integrations
25
Onboarding
1 days

Retell.ai
Score
82
Latency
950 ms
Automation
55%
Integrations
25
Onboarding
1 days
Cost
Low
HIPAA Compliant
Yes

Sierra AI
Score
79
Latency
800 ms
Automation
60%
Integrations
30
Onboarding
7 days
Cost
Low
HIPAA Compliant
Yes
Retell.ai
Retell AI offers fast, scalable voice agents with response times under a second and impressive developer flexibility. You can bring your own LLM, customize behavior deeply, and monitor everything through real-time dashboards. It’s well-suited for teams with in-house engineering that want control and scale. But the learning curve is real—getting up and running takes work, integrations often require custom scripts, and pricing isn’t transparent. While it performs well under the hood, Retell isn’t the most approachable platform for teams seeking simplicity or industry-ready templates out of the box.
Sierra AI
Sierra AI delivers a comprehensive conversational platform with multi-channel voice and chat, real-time analytics, and enterprise-grade security out of the box. But you won’t find a price list anywhere—expect to negotiate usage-based fees that climb steeply as you add advanced features or extra channels. Its “build once, run everywhere” Agent OS sounds neat, but customizing flows and integrating with legacy systems often requires dedicated engineering time. The command center offers deep controls, yet teams frequently find it overengineered for routine tasks and in need of training to manage. And despite claims of empathetic, human-like responses, at scale the agents can still stumble over accents or complex queries, leaving gaps that demand human intervention.
Full Comparison
Vendor | Score | Latency | Automation | Integrations | Cost | Action |
---|---|---|---|---|---|---|
OpenCall.ai $0.10/ minute | 93 | 700 ms | 76% | 2000 | Low | |
![]() Retell.ai $0.07 – 0.08 /min | 82 | 950 ms | 55% | 25 | Low | |
![]() Sierra AI $2 per successful outcome | 79 | 800 ms | 60% | 30 | Low | |
![]() PolyAI $0.25 /min (example case study) | 67 | 1700 ms | 72% | 25 | Medium | |
![]() Bland AI $0.09/min | 66 | 1100 ms | 50% | 15 | Low | |
![]() Phonely $396 (yearly) | 61 | 1200 ms | 52% | 17 | Medium | |
![]() Hey Rosie $49/mo (250 min) + $0.25/min | 57 | 950 ms | 60% | 1 | Low | |
![]() Smith.ai $3.25 /call (Starter 30 calls @ $97.50/mo) | 55 | 2300 ms | 40% | 30 | Medium | |
![]() 8x8 XCaaS $60 per seat per month | 49 | 250 ms | 50% | 15 | Medium | |
![]() CloudTalk $25 – $50 /user/mo | 47 | 23 ms | 40% | 500 | Low | |
Synthflow AI $0.08 /min (Growth) | 20 | 2300 ms | 45% | 20 | Low | |
![]() Balto.ai $100 / seat /mo | 12 | 100 ms | 0% | 40 | High |