Lead Qualification
Instantly screen inbound contacts, confirm match criteria, and log results.
00:00
A monday.com company
Two developer voice AI platforms side by side, with Harmony.ai as the managed option for teams handling 500+ calls a month. Every fact comes from the vendors’ own sites and docs.
Name
Work email
Phone Number
Retell AI vs Vapi vs Harmony.ai
 |  |  | |
|---|---|---|---|
| Platform | |||
| Built for | General-purpose voice agents for phone, web, SMS | Developer platform for building voice agents, API-first | Revenue teams: AI receptionist, AI SDR, scheduling |
| Model | Bring your own: choose the LLM and TTS provider per agent | Bring your own: choose the LLM and TTS provider per agent | Our own models, built for the phone |
| Sounds human | Choice of seven TTS providers; platform voices fine-tuned for phone; LLM is bring-your-own | Bring-your-own TTS: ElevenLabs, PlayHT, Cartesia and others, plus your own cloned voices | Our own conversation models handle interruptions, timing and tone, so calls feel human |
| Implementation | Self-serve | Self-serve; enterprise deployment support on Scale plan | White-glove |
| Calling & scale | |||
| Latency | ~600ms latency (published) | Sub-500ms average (published) | Sub-400ms median response |
| Concurrency | 20 concurrent by default on pay-as-you-go; burst surcharge | 10 concurrent included, $10 per line/month extra; custom on Scale | 1 to 10,000 parallel calls |
| Telephony | Buy Retell-managed US and Canada numbers in the dashboard, or bring your own over SIP trunking | Up to 5 free US numbers with daily outbound caps; import Twilio, Vonage or Telnyx numbers or bring a SIP trunk to scale | Built-in telephony or bring your own trunks; buy, assign and retire numbers across regions from one inventory; port or forward |
| Spam remediation | Verified phone number registration and branded call, US only, as paid add-ons | Docs walk you through registering STIR/SHAKEN and CNAM with your own carrier; nothing managed | Number-reputation monitoring, automatic quarantine of flagged numbers, remediation, branded caller ID and local presence |
| IVR, screeners and gatekeepers | Press Digit tool for outbound IVR menus, IVR and voicemail detection, inbound DTMF capture; nothing documented for human gatekeepers | DTMF keypad tool for IVR menus, voicemail detection with fallback providers; nothing documented for human gatekeepers | Navigates external phone trees, hold queues and human gatekeepers to reach the right party; DTMF both ways; voicemail detection and retry |
| Insight & improvement | |||
| Reporting | Analytics dashboard with custom charts; post-call analysis with custom extracted fields | Analytics dashboard and API with custom queries; call logs and transcripts | Funnel, call-flow and conversation analytics on 100% of calls; ask for a report in plain language and get it built on the spot |
| Self-improvement | Manual: review post-call analysis, edit the prompt, re-test | Manual: review calls, edit the assistant, re-run test suites | Reasoning trace on every call, simulate changes on past calls, agent proposes knowledge-base updates you approve |
| Experimentation | A/B test by splitting live traffic between agents or prompts; simulation test cases | Test suites and evals for regression testing; no built-in traffic-split A/B documented | A/B live or synthetic traffic, publish the winner, roll back; agent keeps what converts across a campaign |
| Pricing & compliance | |||
| Pricing | Pay-as-you-go, $0.07–$0.31/min plus add-ons; enterprise custom | $0.05/min platform fee plus model costs at cost; HIPAA add-on $2,000/mo | Plans start at $3K/month |
| Compliance | HIPAA, SOC 2 Type 1 and 2, GDPR, ISO 27001 | SOC 2, HIPAA (paid add-on), PCI | SOC 2 Type II, HIPAA, GDPR, ISO 27001 |
Retell AI and Vapi figures from retellai.com, docs.retellai.com, vapi.ai and docs.vapi.ai, checked 9 Sep 2026. Retell AI and Vapi are trademarks of their owners. Harmony.ai is not affiliated with either.
Hear it on your own use case.
Four quick questions, then we’ll configure an agent on your use case and let you listen before you commit to anything.
Built for revenue, not a toolkit
Inbound and outbound on one platform. The agent dials, qualifies, and books meetings in your CRM.
Implementation is included
White-glove setup, live in days. No engineering project to stand up telephony, models, and workflows.
Every call becomes data
Every call transcribed and scored. Warm transfers with context, PII redaction, TCPA and DNC aware.
Scale without a quota request
1 to 10,000 parallel calls. Sub-400ms median response at any volume.
Meet Siena, your AI assistant
Enterprise-grade security
Enterprise-grade AI infrastructure with built-in protection and security, data privacy, governance, permissions, and compliance.
