Vapi vs Retell AI: Best Platform for Building Voice Agents?

If you are building an AI voice agent in 2026, two developer platforms dominate the shortlist: Vapi and Retell AI. Both bill per minute, both let you assemble a stack from your choice of speech-to-text, LLM, and text-to-speech, and both connect to real phone numbers over SIP. The difference is philosophical: one hands you an unopinionated orchestration layer, the other hands you a curated, low-code path to a working agent. This guide breaks down where each wins.

Quick comparison

Vapi

Vapi is an orchestration layer, not a managed product. It sits between your telephony provider, your chosen models, and your application logic, and it lets you swap any component. Want Deepgram Nova-3 for transcription, GPT-4o-mini for reasoning, and ElevenLabs Flash for the voice? Vapi wires them together and manages the real-time turn-taking, interruption handling, and streaming for you. This modularity is the core reason larger engineering teams reach for it: nothing about the stack is locked, and you can chase latency or cost by mixing and matching providers.

The developer experience is API-first. You define assistants programmatically, attach tools and function calls, and control the conversation flow in code rather than clicking through a builder. On telephony, Vapi connects to Twilio and Vonage and supports SIP trunking, so you can bring existing numbers. When tuned with a lean stack, Vapi reaches roughly 500-700ms median latency, and on measured median time-to-first-audio-byte it tends to edge out Retell (around 1,558ms vs 1,740ms in one 2026 benchmark).

Real limits: the flexibility is also the tax. Because Vapi only prices the orchestration layer, you assemble and pay for every other piece yourself, which means more moving parts to configure, monitor, and debug. Getting to that tuned latency figure requires deliberate provider selection; the defaults are not automatically optimal. HIPAA and other compliance guarantees sit behind a custom, undisclosed enterprise contract rather than being available on the pay-as-you-go tier, which matters for healthcare or regulated workloads.

Price: advertised from ~$0.05/min for the orchestration layer, with realistic all-in costs of roughly $0.07-$0.33/min once STT (~$0.01), the LLM (~$0.02-$0.20), TTS (~$0.04), and telephony (~$0.01) are added. Premium voices and large models can push past $0.30/min. Pay-as-you-go has no mandatory base subscription.

Retell AI

Retell AI runs a managed stack with curated model choices and publishes a single all-in price for the result. You still choose your LLM, voice engine, and telephony provider from supported options, but Retell handles the orchestration and, critically, ships a no-code visual builder for designing conversation flows. That combination is why solo developers and small teams often get to a working agent faster here: much of the tuning that Vapi expects you to do by hand is baked into sensible defaults.

Out of the box, Retell measures around 600ms end-to-end latency with no tuning required, and it supports barge-in for natural interruptions. It deploys agents across phone calls, web calls, SMS, and chat, and integrates with CRMs, calendars, automation tools like Make and n8n, and telephony providers including Twilio and Vonage with SIP support. The standout for regulated teams is compliance: Retell states it is HIPAA, SOC 2 Type II, and GDPR compliant, and those protections apply across plans rather than being gated behind an enterprise tier. It also includes 20 free concurrent calls, which is generous for testing and early production.

Real limits: the curated approach means less freedom to drop in an arbitrary model or provider that Retell does not support, so teams chasing a very specific cost or latency profile may hit a ceiling. The pricing also carries small fixed add-ons that Vapi does not surface the same way: $2 per month per phone number and $8 per month for each concurrent call beyond the free 20, which adds up for high-concurrency deployments. Like Vapi, it is voice-first; neither platform natively handles WhatsApp or website chat as a first-class channel.

Price: advertised from ~$0.07/min for the voice infrastructure layer, with typical production setups landing at ~$0.13-$0.31/min once TTS, the LLM, and telephony are included. Add $2/mo per number and $8/mo per extra concurrent call. No mandatory base subscription.

Which should you pick?

The honest answer is that both platforms are built on the same idea and both work. The decision comes down to how much control you want versus how fast you want to ship. Vapi is the right call when your team has the engineering appetite to tune each layer and wants nothing locked down. Retell is the better default when you want a natural-sounding agent running quickly, with compliance and reasonable latency handled for you.

• Pick Vapi if you have an engineering team that wants full control over the STT, LLM, and TTS stack, plans to tune latency and cost aggressively, and prefers defining agents in code.
• Pick Retell AI if you are a solo dev or small team who wants a working agent fast, values a no-code flow builder, or needs HIPAA/SOC 2/GDPR compliance without an enterprise contract.

FAQ

Which is cheaper at scale? They are close. Vapi's floor is lower (~$0.05 base vs ~$0.07), but real all-in costs overlap heavily once you add models and telephony, roughly $0.07-$0.33/min for Vapi and $0.13-$0.31/min for Retell. At high concurrency, Retell's $8/mo per extra concurrent call adds a fixed cost Vapi does not charge the same way, so model your expected concurrency and minutes rather than comparing headline rates.

Can I use my own phone numbers and telephony? Yes on both. Vapi and Retell each connect to Twilio and Vonage and support SIP trunking, so you can port or route existing numbers. Retell adds a $2/month per-number fee; Vapi passes telephony through at roughly $0.01/min on top of the provider's own charges.

Do I need to be a developer, or is there a no-code option? Retell ships a no-code visual builder for designing conversation flows, so non-engineers can assemble and test an agent. Vapi is API-first and expects you to define assistants in code, which suits developers who want programmatic control. If you want to avoid writing code, start with Retell; if you want everything scriptable, start with Vapi.