VAPI vs Retell AI - Which Voice AI Platform Wins in ?
Businesses implementing voice AI face a critical choice between platforms - Retell AI's no-code simplicity or VAPI's developer-friendly customization. We tested both across 7 key areas to determine which delivers better results for different use cases.
Ease of Use Comparison
Building voice AI agents shouldn't require an engineering degree, yet many platforms overwhelm non-technical users with complex interfaces and API-focused workflows. In our testing, Retell AI emerged as the clear winner for ease of use with its visual canvas approach to conversation design.
The platform provides pre-built templates and a drag-and-drop interface that lets you construct conversational flows by connecting nodes. Each node represents a step in the conversation where you can enter prompts or static responses. This visual approach makes it immediately clear how the conversation will flow and allows for easy adjustments.
Key insight: Retell AI's "conversational flow agent" approach breaks down large prompts into smaller, contextual pieces distributed across nodes. This not only makes building easier but improves latency by only sending relevant context to the LLM at each step.
VAPI has traditionally been more developer-focused, requiring you to work with a single massive prompt. However, their recent "workflows" feature introduces a similar visual builder that makes the platform more accessible. While still not as polished as Retell AI's interface, it represents significant progress in usability.
Telephony Options
Connecting real phone numbers to your voice agent is critical for business use cases. Both platforms handle telephony differently, with Retell AI offering more built-in functionality while VAPI provides greater flexibility.
Retell AI makes it simple to purchase phone numbers directly within the platform at $2/month per number. The system handles all the telephony infrastructure, including a generous default concurrency of 20 simultaneous calls. For businesses outside the US/Canada, you'll need to import numbers via Twilio or similar services.
Standout feature: Retell AI's "concurrency burst" automatically scales to handle up to 60 concurrent calls during peak periods without requiring permanent line purchases - you just pay a slightly higher rate during bursts.
VAPI provides 10 free US numbers but restricts their use for outbound campaigns. For production use, you'll need to bring your own numbers via Twilio or other providers. The platform defaults to 10 concurrent calls, with additional lines costing $10/month each.
Voice Realism
Voice quality can make or break user acceptance of your AI agent. Both platforms integrate with ElevenLabs for premium voice synthesis, but implement the integration differently.
Retell AI uses ElevenLabs as its default voice engine and provides straightforward options for voice cloning. You can either upload audio samples to create an instant voice or connect an existing ElevenLabs voice using your API key. The platform also supports other options like Cartesia and Mimic3, but ElevenLabs delivers the best results.
VAPI similarly integrates with ElevenLabs but offers more voice engine choices including its own proprietary voices. In our testing, VAPI's default voices were surprisingly good, though most businesses will still prefer ElevenLabs for premium quality.
Testing advantage: Both platforms provide in-browser testing that doesn't require making actual phone calls - saving time and credits during development.
Integration Capabilities
Voice agents rarely operate in isolation - they need to connect with CRMs, calendars, and other business systems. Here the platforms take different approaches to integrations.
Retell AI focuses on flexibility through webhooks and MCP (Model Context Protocol) connections rather than pre-built integrations. While this means you can connect to virtually any system, it requires more technical work. The platform only offers one native integration with Cal.com for calendar functionality.
VAPI provides better native integrations including Slack, Google Sheets, and Google Calendar. Their "tools" system lets you build reusable integrations that can be attached to multiple agents. For developers, the API is exceptionally well-documented and designed for extensibility.
Developer note: VAPI's API design reflects its origins as "Voice API" - it's clearly built by developers for developers, with thoughtful architecture and excellent documentation.
Call Concurrency Handling
Businesses with fluctuating call volumes need platforms that can scale seamlessly. Our testing focused on how each platform handles concurrent calls and peak periods.
Retell AI's default 20 concurrent calls is generous, and their burst feature automatically scales to 60 calls during peaks. For consistently high volumes, you can purchase additional lines at $8 each. The platform clearly displays current usage and makes it easy to adjust capacity as needed.
VAPI starts with just 10 concurrent calls, requiring $10/month per additional line. There's no burst functionality - you must purchase sufficient lines to handle your peak volume. While this gives predictable performance, it can become expensive for businesses with highly variable call patterns.
Latency Performance
Latency - the delay between when a user speaks and when they hear a response - critically impacts conversation flow. We measured end-to-end latency across multiple test calls on both platforms.
VAPI delivered the lowest latency at just 536 milliseconds on average - the fastest we've seen from any voice AI platform. The platform provides detailed latency breakdowns showing where delays occur (transcription, LLM processing, or voice synthesis) to help optimize performance.
Retell AI averaged 714 milliseconds in our tests - still very good and within the range of natural conversation. The platform uniquely shows estimated latency during development, helping you identify potential bottlenecks before deployment.
Transparency win: Both platforms provide exceptional visibility into latency sources - a rarity in voice AI that demonstrates their engineering-focused approach.
Pricing & Hidden Costs
Voice AI costs can add up quickly between telephony, LLM usage, and platform fees. We analyzed pricing for a typical business use case (3,000 call minutes/month) on comparable configurations.
VAPI emerged as the more affordable option at approximately 9-10 cents per minute total cost. Their pricing model charges a 5 cent/minute platform fee plus the cost of any services you use through them (like ElevenLabs voices). You can reduce costs further by bringing your own API keys.
Retell AI averages about 13 cents per minute for similar configurations. While more expensive, this includes more features in the base price rather than requiring add-ons. The platform does have some potential hidden costs like $1,000/month for HIPAA compliance if needed.
Cost saver: VAPI's ability to use your existing API keys (for ElevenLabs, OpenAI, etc.) can significantly reduce costs compared to platforms that require purchasing through them.
Watch the Full Comparison
See both platforms in action with live demos and side-by-side testing of key features like call handling, voice quality, and integration setups (jump to 4:30 for the latency comparison tests).
Key Takeaways
After extensive testing across seven critical factors, our recommendation depends on your specific needs and technical capabilities.
In summary: Choose Retell AI for no-code ease of use and superior call handling. Choose VAPI for lowest latency, best integrations, and most affordable pricing. Both platforms offer free trials - we recommend testing both with your specific use case.
For businesses prioritizing simplicity and needing to handle variable call volumes, Retell AI's visual builder and concurrency burst make it the better choice. Development teams and businesses needing tight integrations or the lowest possible latency will prefer VAPI's customizable platform.
Frequently Asked Questions
Common questions about voice AI platforms
Retell AI is significantly easier for non-technical users with its visual canvas interface for building conversational flows. The platform provides templates and a more guided experience compared to VAPI which is designed primarily for developers.
Retell's node-based approach lets you see the entire conversation flow visually, making it easier to understand and modify. VAPI's new workflows feature does make it more accessible than before, but still requires more technical understanding for advanced configurations.
- Retell AI: Best for marketing teams, sales ops, and business users
- VAPI: Better suited for developers and technical teams
- Both offer free trials to test usability with your team
Retell AI provides built-in phone number purchasing ($2/month) and handles call concurrency better with burst capacity up to 60 concurrent calls. The platform makes it easy to manage numbers and scale capacity as needed.
VAPI offers 10 free US numbers but requires external services like Twilio for production use. While more flexible in terms of provider choice, this adds complexity to setup and management.
- Retell: Better for businesses that want everything in one platform
- VAPI: More flexibility to use existing telephony providers
- Both support inbound and outbound calling
VAPI had significantly lower latency in our tests at 536ms end-to-end compared to Retell AI's 714ms. This difference is noticeable in conversation flow, with VAPI feeling more immediate and natural.
Both platforms provide excellent latency breakdowns to help optimize performance. VAPI's infrastructure is specifically optimized for speed, while Retell AI offers more tools to reduce latency through prompt optimization.
- VAPI: Fastest overall performance
- Retell: Better tools for latency optimization
- Both under 800ms - acceptable for natural conversation
VAPI is generally more affordable at 9-10 cents per minute compared to Retell AI's 13 cents per minute for similar configurations. VAPI's pricing model allows bringing your own API keys which can further reduce costs.
Retell AI includes more features in its base pricing, so the value comparison depends on which features you need. For high-volume use cases, VAPI's per-minute savings become significant.
- VAPI: Lowest cost for equivalent functionality
- Retell: More inclusive pricing for core features
- Both offer free tiers for testing
VAPI has better native integrations including Slack, Google Sheets, and Google Calendar. The platform is designed to connect with other systems, offering both pre-built connectors and flexible API options.
Retell AI primarily relies on webhooks and MCP connections. While this provides ultimate flexibility, it requires more technical work to implement common business integrations compared to VAPI's ready-made options.
- VAPI: Best for businesses needing many integrations
- Retell: More flexible but requires development work
- Both can connect to any system with proper implementation
Both platforms use ElevenLabs for premium voice quality and allow custom voice cloning. When configured identically with the same ElevenLabs voice options, we found no meaningful difference in output quality.
Retell AI makes voice cloning slightly easier with direct audio uploads in the platform. VAPI offers more voice engine choices beyond ElevenLabs, including its own proprietary voices that are surprisingly good.
- Equal quality when using same ElevenLabs configuration
- Retell: Easier voice cloning process
- VAPI: More voice engine options available
Retell AI handles high-volume calling better with its concurrency burst feature that automatically scales to 3x your normal limit during peak periods. This provides flexibility without requiring permanent capacity purchases.
VAPI requires purchasing additional lines at $10/month each for increased capacity. While this gives predictable performance, it can become expensive for businesses with highly variable call patterns.
- Retell: Best for unpredictable call volumes
- VAPI: More predictable but less flexible scaling
- Both can handle 100+ concurrent calls with proper configuration
GrowwStacks helps businesses implement voice AI solutions tailored to their specific needs. We handle the entire process from platform selection to deployment and optimization.
Our team can build custom voice agents on either VAPI or Retell AI platforms, integrate them with your existing systems, and ensure they're optimized for your call volume and use case. We provide ongoing maintenance and support to keep your solution running smoothly.
- Free consultation to assess your requirements
- Custom development for your specific use case
- Ongoing support and optimization services
Ready to Implement Voice AI for Your Business?
Every day without automated call handling costs your team valuable time. GrowwStacks can have a custom voice AI solution deployed for your business in as little as 2 weeks.