Retell AI
A developer platform for building production-grade voice AI agents that handle phone conversations with human-like latency and natural turn-taking.
Overview
Retell AI is a developer-first platform for creating voice AI agents that can hold natural phone conversations. Unlike chatbot builders that bolt on voice as an afterthought, Retell was designed from the ground up for real-time telephony — its agents respond in under 800 milliseconds, handle interruptions gracefully, and manage conversational turn-taking in a way that feels genuinely human.
The platform sits between your LLM of choice (OpenAI, Anthropic, or your own) and telephony infrastructure, handling the hard parts: speech-to-text, text-to-speech, conversation orchestration, and phone system integration. You define the agent's personality, knowledge base, and call flow logic through an API or visual builder, and Retell handles the rest — including transferring to human agents when needed.
What sets Retell apart from competitors like Bland AI or Vapi is its production readiness. The platform is HIPAA-compliant, processes millions of calls, and has documented case studies showing 50-70% cost reductions in customer service operations. For teams building voice AI at scale, it's currently the most mature option available.
Key features
Voice AI Agents
Build conversational voice agents that handle inbound and outbound phone calls with natural speech patterns, backchanneling, and human-like pacing.
Sub-800ms Latency
End-to-end response times under 800 milliseconds for natural conversational flow. Proprietary orchestration layer minimizes the gap between speech recognition and agent response.
Phone Integration
Native telephony integration with number provisioning, call transfer, DTMF handling, and voicemail detection. Works with Twilio, Vonage, and direct SIP trunks.
Multi-LLM Support
Bring your own LLM — supports OpenAI, Anthropic Claude, open-source models, or custom fine-tuned models. Swap models without changing your agent logic.
Pricing
Free tier: $10 free credit to test the platform — enough for roughly 140 minutes of calls
| Plan | Price | What's included |
|---|---|---|
| Free Trial | Free | $10 in credits to start, full API access, all features included |
| Pay As You Go | ~$0.07/min | Usage-based pricing, no monthly commitment, all core features |
| Enterprise | Custom | Volume discounts, dedicated support, SLAs, HIPAA BAA, custom deployment |
$10 in credits to start, full API access, all features included
Usage-based pricing, no monthly commitment, all core features
Volume discounts, dedicated support, SLAs, HIPAA BAA, custom deployment
Pros & cons
Pros
- ✓Sub-800ms latency makes conversations feel genuinely natural, not robotic
- ✓HIPAA-compliant with enterprise security certifications for regulated industries
- ✓Bring-your-own-LLM means you're not locked into a single AI provider
- ✓Extensive telephony features including call transfer, voicemail detection, and SIP support
Cons
- ×Requires developer skills — no true no-code builder for non-technical users
- ×Usage-based pricing can get expensive at high call volumes without enterprise negotiation
- ×Voice customization options are more limited than dedicated TTS platforms like ElevenLabs
- ×Documentation could be more thorough for advanced use cases like custom SIP integrations