Side-by-side comparison to help you choose the right tool for your business
Our Verdict: Vapi for maximum flexibility, Retell AI for the most natural conversations
Both Vapi and Retell are developer-first voice AI platforms, but they optimize for different things. Vapi gives you the most control — choose any LLM, any voice provider, and orchestrate complex multi-agent flows via API. Retell AI optimizes for conversation quality — sub-800ms latency, best-in-class interruption handling, and natural turn-taking that makes callers forget they're talking to AI. Pick Vapi if flexibility and integration matter most. Pick Retell if conversation naturalness is your priority.
Developers who need full control over voice agent architecture
$0.05/min (platform) + voice + LLM costs (~$0.10-0.18/min total)
advanced
5-14 days
Teams prioritizing natural conversation quality and low latency
$0.07-0.14/min (platform) + LLM costs (~$0.08-0.17/min total)
advanced
5-10 days
| Feature | Vapi | Retell AI |
|---|---|---|
| End-to-end latency | ~1-1.5 sec | < 800ms |
| Interruption handling | Configurable | Best-in-class (natural) |
| Voice providers | 10+ (choose per agent) | Multiple (curated selection) |
| LLM flexibility | Any LLM with API | Any LLM with API |
| Call analytics | Via server events | Built-in dashboard + sentiment |
| Call transfer | Warm + cold | Warm + cold + conference |
| Function calling | Yes (server-side) | Yes (server-side) |
| Multi-language | Depends on voice provider | 30+ languages |
Complex routing logic across departments, queue management, and integration with existing PBX systems. Vapi's programmable pipeline handles the orchestration.
Patients need to feel comfortable talking to the AI. Retell's sub-800ms latency and natural interruption handling make conversations feel human.
WebSocket integration embeds voice into the app's existing architecture. Vapi's 10+ voice providers let you pick the voice that matches the brand.
Sensitive conversations require natural pacing and the ability to handle interruptions gracefully. Retell's sentiment analysis flags calls that need human escalation.
We implement both options. Tell us your use case and we'll recommend the right fit — then set it up for you.
Humans expect responses within 500ms in natural conversation. Every 100ms above that makes the AI feel more robotic. At 800ms (Retell), most callers don't notice. At 1.5 seconds (Vapi default), there's a noticeable pause that signals 'this is a bot.' For sales and support calls, this perception gap directly impacts conversion rates.
Partially. By choosing fast components (Deepgram STT + GPT-4o-mini + PlayHT Turbo), Vapi can hit ~900ms-1 second. But Retell's architecture is optimized end-to-end for latency in ways that component selection alone can't replicate. If sub-second latency is critical, Retell has the architectural advantage.
Comparable difficulty. Both are API-first and require developer skills. Retell's documentation is more beginner-friendly with step-by-step guides. Vapi's community is larger with more code examples on GitHub. Plan for 1-2 weeks either way for a production-quality agent.
Vapi: $500 (platform) + $300-800 (voice) + $100-300 (LLM) = $900-1,600/month. Retell: $700-1,400 (platform) + $100-300 (LLM) = $800-1,700/month. At scale they're remarkably similar. The decision should be based on technical requirements, not pricing.