Retell AI vs. Vapi: Which Voice Agent Platform Should You Actually Build On?

I've built voice agents on both Retell AI and Vapi. Here's what nobody tells you before you commit to one.

A client came to me last month, a healthcare clinic in Nairobi needing an AI receptionist. Something that could book appointments, answer common questions, and handle patient intake over the phone. 24/7. In Swahili and English.

I'd built similar systems before. But this time I had a real decision to make: Retell AI or Vapi?

Both are impressive platforms. Both can build a voice agent in a fraction of the time it would've taken three years ago. But they're built for different people, and choosing the wrong one will cost you weeks.

Here's what I learned, and the decision framework I now use for every voice agent project.

Retell AI, Built for Speed, Optimized for Production

Retell AI is the platform you choose when you need something running fast and want it to sound human. The voice quality is genuinely impressive, natural pacing, realistic filler sounds, good emotional range. For a healthcare receptionist talking to patients who aren't tech-savvy, that matters enormously.

The dashboard is clean and the abstractions make sense. You can connect a phone number, define your agent's personality and workflow, and be live in an afternoon. For non-technical stakeholders, showing them a working Retell AI demo is easy, they immediately "get it."

Key features:

• Pre-built templates for common use cases (customer service, scheduling, lead qualification)
• Low-latency voice with natural interruption handling
• Built-in call recording and analytics dashboard
• Twilio integration for phone number management
• Webhook support for CRM integration

The trade-off: Retell AI is more opinionated. It has a preferred way to do things, and when you need to deviate, say, a custom Mpesa payment confirmation flow mid-call, you're fighting the framework. Custom function calling is supported but less flexible than Vapi.

Pricing: Starts at ~$0.07/minute for voice. Free tier available for testing.

Best for: Production voice agents, client demos, healthcare/hospitality/customer service, any project where voice quality and time-to-deploy matter most.

Vapi, Built for Developers Who Want Full Control

Vapi is the platform you choose when you know exactly what you're building and need every dial turned to your specification. It's lower-level than Retell AI, which means more setup but also more flexibility.

Want to inject real-time data mid-conversation? Route calls based on a database lookup? Build a multi-step outbound calling sequence with conditional branching? Vapi handles all of that cleanly.

Key features:

• Full control over LLM, voice provider, and transcription engine (mix and match)
• Native n8n and Make.com webhook integration
• Server-sent events for real-time call monitoring
• Squad agents (multiple AI agents on one call)
• Custom tools and function calling with full parameter control

The voice quality is solid, not quite at Retell AI's level of naturalness out of the box, but configurable enough to get close if you spend time on it. The learning curve is steeper, and you'll spend more time in documentation.

Pricing: Starts at ~$0.05/minute plus voice provider costs. More granular billing. For a full cost breakdown by use case, see my voice agent cost calculator.

Best for: Complex, custom voice agents, outbound calling sequences, developer teams, n8n/Make integrations, projects where you need the AI to make real-time decisions based on external data.

Head-to-Head Comparison

Building for African Markets, What Changes

Both platforms work for African markets, but there are things to know:

1. Latency: International server routing adds 200–400ms. For voice AI, that's noticeable. With Retell AI you have less control over this; with Vapi you can specify server regions closer to your users.
2. Languages: Both support Swahili via Whisper transcription, but code-switching (switching between Swahili and English mid-sentence, which is normal in Nairobi) still causes issues on both platforms. Route by detected language at call start as a workaround.
3. Phone number provisioning: Both support Twilio for African phone numbers (+254 Kenya, +234 Nigeria, etc.). Budget for Twilio costs separately from the platform cost.
4. Mpesa integration: Neither platform has native Mpesa support. You'll need to handle payment flows via webhooks to your n8n workflow, then have the AI confirm the payment verbally after your backend verifies the Daraja callback.

My Decision Framework

Use Retell AI when:

• Client needs a demo within days
• Voice naturalness is the top priority
• The use case is straightforward (booking, FAQ, intake)
• Non-technical staff will manage it post-launch
• Budget is tight and you need predictable per-minute pricing

Use Vapi when:

• You need real-time data injection mid-call
• Complex outbound sequences with branching logic
• You want to use a specific LLM (GPT-4o, Claude, etc.)
• Building for developers or technical teams
• n8n is core to your stack and you want native integration

The Verdict

For the Nairobi clinic, I went with Retell AI. Patients needed a voice that sounded natural and trustworthy. The clinic's staff needed something they could maintain without calling me every week. Retell AI delivered both. You can read the full case study to see how it performed after launch.

For a fintech client needing an outbound loan reminder agent with dynamic data injection and Mpesa callbacks, Vapi was the right call, the flexibility was worth the extra build time.

If you're building your first voice agent: start with Retell AI. If you've shipped one before and you know what you need: consider Vapi.

The era of AI answering your business phone is here. The question is just which tool fits your situation.