Vapi vs Retell AI — Which Voice Platform Should You Build On?
Vapi and Retell AI are the two dominant voice AI infrastructure platforms in 2025. Both power production AI phone agents — but they are built for different teams and different use cases. This comparison covers latency, pricing, LLM flexibility, ease of deployment and which platform SCALE D2C recommends for D2C brands.
SCALE D2C's Honest Recommendation
Vapi wins on technical depth, LLM flexibility, sub-500ms latency and developer ecosystem. Retell AI wins on ease of use, out-of-the-box conversation quality and speed to production. For D2C brands: choose Vapi if you have in-house technical capability; choose Retell if you need it live fast without a developer.
Vapi vs Retell AI — Feature by Feature
| Feature | Vapi | Retell AI |
|---|---|---|
| Voice Latency | < 500ms — best in class ▲ | < 700ms — excellent |
| LLM Flexibility | Any — GPT-4o, Claude, Llama, custom ▲ | GPT-4o, Claude, Gemini |
| Voice Synthesis | ElevenLabs, Deepgram, Azure, OpenAI | ElevenLabs, Deepgram, Azure |
| Ease of Setup | Developer-heavy, deep config required | Simple — live in hours ▲ |
| Conversation Quality | Excellent (depends on prompting) | Excellent out-of-the-box ▲ |
| Custom Function Calling | Deep + webhooks, fully configurable ▲ | Function calling + webhooks |
| Telephony | Twilio, Vonage, or Vapi numbers | Built-in + Twilio compatible |
| Pricing per minute | ~$0.05–0.10 + LLM cost | ~$0.07–0.13 all-in |
| Analytics | Detailed call logs + transcripts | Clean dashboard + transcripts |
| Multi-language | 100+ via TTS/STT choice | 100+ languages |
| Documentation | Comprehensive, developer-first ▲ | Good, more accessible |
| Community & Support | Large Discord, very active ▲ | Smaller but responsive |
| Interruption Handling | Advanced — highly configurable ▲ | Good native handling |
| Self-hosted Option | Yes — on-prem available ▲ | No |
Which Platform Sounds More Natural?
Both Vapi and Retell AI achieve sub-second latency in production — the threshold for natural-feeling conversation. Vapi achieves under 500ms average end-to-end latency through aggressive audio streaming and parallel processing. Retell averages 600–700ms, still imperceptible in most conversational contexts. For voice quality, both support ElevenLabs for premium synthesis. The key difference is interruption handling: Vapi's detection is more configurable and handles aggressive interrupters better. For D2C customer service where callers commonly interrupt, this matters in production.
Flexibility vs Simplicity in the Brain
Vapi's LLM flexibility is its strongest differentiator. You can use GPT-4o, Claude 3.5 Sonnet, Llama 3, Mistral, or any custom-hosted model — and switch between models per call without changing telephony infrastructure. Retell AI supports major commercial models (GPT-4o, Claude, Gemini) with less granular control over model parameters. For D2C brands running standard customer service workflows, both have sufficient LLM support. For teams wanting open-source models for cost efficiency or needing custom model integration, Vapi's flexibility is a significant advantage.
Hours vs Days to First Call
Retell AI genuinely wins here. Its agent builder and documentation are designed for a broader audience — a non-developer product manager can build a working prototype in hours. Vapi requires technical depth: WebSocket connections, custom function schemas and telephony provider configuration. SCALE D2C recommends Retell AI for clients with limited engineering resource who need voice agents quickly, and Vapi for clients with strong technical teams who need maximum control. The 10× complexity difference in initial setup is real and should drive platform selection.
Real Cost Comparison for D2C Brands
Both platforms use consumption-based pricing. Vapi charges approximately $0.05–0.10 per call minute plus underlying LLM and TTS costs paid separately to OpenAI, Anthropic and ElevenLabs. Retell AI bundles more into its per-minute rate (~$0.07–0.13 all-in including baseline LLM). At low volumes, Retell's bundled pricing is simpler. At high volumes (100,000+ minutes/month), Vapi's unbundled model lets you optimise each cost component separately — typically resulting in lower total cost. For D2C brands handling 10,000–50,000 calls per month, the cost difference is minimal; platform decision should be driven by technical fit.
"SCALE D2C recommended Vapi for our enterprise setup and had our first voice agent handling real customer calls within 3 weeks. 78% of inbound calls now resolve without a human agent."
Frequently Asked Questions
Vapi is a developer-first platform with maximum LLM flexibility, sub-500ms latency and deep customisation — requiring significant technical expertise to configure. Retell AI is designed for faster deployment with excellent out-of-the-box conversation quality and a more accessible setup process. Both platforms are production-grade; the choice depends on your technical capability and use case complexity.
For D2C brands with in-house technical teams, SCALE D2C recommends Vapi for its latency performance, LLM flexibility and self-hosting option. For brands without dedicated engineering resources who need a production voice agent fast, Retell AI delivers significantly faster. In either case, SCALE D2C manages the full deployment — so platform selection is driven by your technical requirements.
Yes, though it requires rebuilding your agent configuration on the new platform. Your conversation flows, system prompts and function definitions are partially portable, but the configuration format differs between platforms. SCALE D2C designs agent architectures that minimise platform lock-in where possible.
At typical D2C volumes (under 50,000 minutes/month), pricing is comparable — roughly $0.08–0.15 per minute all-in including LLM and TTS costs. Vapi allows more granular cost optimisation at scale. Platform selection should be driven by conversation performance and capability fit, not pricing.
Yes — both platforms support function calling/tool use, enabling voice agents to query your Shopify API, CRM and any external data source in real time during calls. SCALE D2C builds the middleware integration layer connecting either platform to your full D2C stack, giving agents live access to order status, customer history and product inventory.
Build Your Voice Agent on the Right Platform. Built for D2C.
SCALE D2C deploys production voice agents on both Vapi and Retell AI. Tell us your use case and we'll recommend the right platform and have a working demo ready in 48 hours.