vioscaleAI
Comparison

Retell AI vs Sierra

On the evidence we track, Retell AI leads this comparison with a composite score of 79/100. Scores are only directly comparable because these tools share a category; the full breakdown and every source is below.

Retell AI full profile →Sierra full profile →
Machine formatsMarkdownJSONGraphQLMarkdown is open. JSON and GraphQL need a free key.
★Retell AI79
Sierra55
Score
vioscaleAI score
Retell AI79 / 100medium · 72%
Sierra55 / 100low · 44%
Pricing
Free tier
Retell AI✓
Sierra–
Model
Retell AIfreemium
Sierracommercial
Price level
Retell AIlow
Sierraunknown
Starting price
Retell AI$0.00
Sierra–
Transparent
Retell AI✓
Sierra✗
Integrations
Count
Retell AI1,000
Sierra6
Security
Certifications
Fedramp
Retell AI–
Sierra✓
Gdpr
Retell AI✓
Sierra✓
Hipaa
Retell AI✓
Sierra✓
Iso27001
Retell AI✓
Sierra✓
Pci
Retell AI–
Sierra✓
Soc2
Retell AI✓
Sierra✓
Trust center
Reliability
Sla pct
Retell AI99.9
Sierra–
Market
Availability
Content
Faq
Retell AI7 items
Sierra7 items

Capabilities

Feature-by-feature on the axes that matter for voice ai agents. “-” means undocumented, not absent.

Capabilities
Deployment model
Retell AINo code saas platform
SierraNo code saas platform
Sub second latency and interruption barget in handling
Retell AI✓
Sierra-
Dynamic mid call API function execution
Retell AI✓
Sierra-
Live human handoff and call transfer logic
Retell AI✓
Sierra✓
Emotion prosody and custom voice cloning
Retell AI✓
Sierra-
Inbound reception and ivr routing replacement
Retell AI✓
Sierra-
Outbound dialing and campaign management
Retell AI✓
Sierra-
Post call transcription and CRM sync
Retell AI✓
Sierra✓
Voicemail detection and answering machine drops
Retell AI✓
Sierra-
Twilio vonage bring your own carrier byoc support
Retell AI✓
Sierra-
SOC2 type ii
Retell AI✓
Sierra-
HIPAA compliance for medical appointment setting
Retell AI✓
Sierra✓
Pricing model
Retell AIPer minute usage based
Sierra-

What each one is

The product in its own terms, so the numbers below have context.

Retell AI

Leader

A cloud-based platform that deploys conversational AI agents to handle inbound and outbound phone calls, including lead qualification, appointment booking, call routing, and CRM integration.

Independently observed

Sierra

Sierra enables businesses to create and deploy conversational AI agents across voice, chat, email, SMS, and other channels. The platform uses an outcome-based pricing model where customers pay based on business results delivered rather than traditional fixed fees.

Independently observed

Pricing

List pricing as published by each vendor, with the date we read it. Always verify at the source before you buy.

Retell AI

Leader
from $0.00/messageUsage-basedFree tier

From $0.07/min usage-based pricing. Free tier with $10 credits.

  • Pay-as-you-go$0.07–$0.31/min for voice agents; $0.002+/msg for chat agents
    • 20 concurrent calls included
    • Full platform access
    • Drag-and-drop agent builder
    • Call transfers and routing
    • CRM integration
    • +1 more
  • EnterpriseContact sales
    • Unlimited concurrent calls
    • HIPAA/BAA compliance
    • SSO
    • Custom MSA
    • Custom DPA
    • +3 more
as of verify ↗

Sierra

Outcome-based pricing model (specific tiers not publicly documented)

as of verify ↗

Platform & deployment

Where each product runs and how it can be hosted. A dash means undocumented, not unsupported.

Platforms
Web
Retell AI✓
Sierra✓
Deployment
Cloud / SaaS
Retell AI✓
Sierra✓

Integrations

What each product connects to. Counts come from the vendor's own integration directory where one exists.

In common (1)
  • WhatsApp

Retell AI

Leader
48 total - 47 not shared
  • Twilio
  • Vonage
  • Telnyx
  • Salesforce
  • HubSpot
  • Zoho CRM
  • Zapier
  • n8n
  • Make
  • viaSocket
  • Zendesk
  • Talkdesk
  • RingCentral
  • ServiceTitan
  • Nice
  • Workable
  • Go High Level
  • OpenDental
  • Slack
  • Monday.com
  • Smartsheets
  • Shopify
  • Stripe
  • Xero
  • +23 more
Independently observed

Sierra

6 total - 5 not shared
  • ChatGPT
  • Chat
  • Voice
  • Email
  • SMS
Independently observed
Still deciding?

Retell AI or Sierra: which one depends on you

A composite score cannot know your constraints. Describe them and both get re-weighted against what you actually need, with the evidence behind every position.

Free to run, no account needed to start. How the evaluation works

Comparison generated from independently-sourced facts. Every value links to its source and retrieval date. See the method.