Vapi vs Retell
Both platforms answer a phone call with a model behind it. They disagree about how much of the pipeline you get to touch, and that answers most of the question.
The verdict
Choose Retell when you want a managed pipeline that answers calls fast with a preset flow, and choose Vapi when you need to pick the model, swap the voice vendor, or run a self-hosted LLM.
We build phone agents for clients on both, plus a stack we assembled ourselves from Twilio, Deepgram and OpenAI directly. We pay these bills. Neither platform is the vendor we have to defend.
Retell's conversation runtime is tuned and opinionated, so it answers calls quickly with little setup. Vapi treats every piece, the model, the voice, the telephony, as a part you choose. That control costs you assembly time and some latency.
Where they genuinely differ
Compared on what changes the build, not on feature counts.
| Dimension | Retell | Vapi |
|---|---|---|
| Model choice | A curated list: OpenAI, Anthropic, Google. | Any provider, including a model you host yourself. |
| Voice vendor | Fixed set inside the platform. | Mix ElevenLabs, Cartesia and others per agent. |
| Latency out of the box | Around 600ms, with no tuning needed. | Around 500 to 700ms once tuned by hand. |
| Building a flow | Visual workflow builder: book, transfer, update a CRM. | A visual editor for simple flows; custom logic needs code. |
| Where it runs | Retell's infrastructure. No self-hosted option. | API-first, so it slots into infrastructure you control. |
| Cost per minute | A low headline rate for the voice engine alone; the real per-minute cost climbs once the model and telephony are added. | A low platform fee with provider costs passed through directly, so the total tracks the model and voice vendor you pick. |
| Best fit | One phone number, a defined flow, live soon. | A voice product with its own model and voice choices. |
Retell
Where it wins
- Fast to a working agent. The workflow builder covers booking, transfers and CRM updates without code.
- Consistent latency without hand-tuning a pipeline.
- One vendor to bill, monitor and support.
Where it hurts
- The model list is fixed. No self-hosted LLM, no model your own security team picked.
- The orchestration logic is not yours to change. Unusual conversation shapes fight the builder.
- No option to run the stack in your own infrastructure.
Vapi
Where it wins
- Swap the model, the voice vendor or the telephony provider without waiting on the platform to add one.
- Fits inside infrastructure you already run, since it is API-first end to end.
- The right base when the voice agent is the product, not a single client's phone line.
Where it hurts
- Untuned latency runs slower than Retell's default. Getting to 500ms takes deliberate work.
- Advanced flows, custom LLMs, multi-agent handoffs, need an engineer writing code, not a form.
- Provider costs pass through directly, so the bill depends on choices you made, not a flat rate.
Rules that settle it
Work through these in order. The first one that matches is your answer.
- 01Choose Retell if the job is one phone line answering calls the same way every time, and you want it live this month.
- 02Choose Retell if nobody on your team wants to own model or voice-vendor decisions.
- 03Choose Vapi if you need a specific model, including one your own team hosts, for compliance or cost reasons.
- 04Choose Vapi if the voice agent is a feature inside a larger product you already control.
- 05Choose neither if the volume does not justify a model call per turn. A scripted IVR handles a narrow, fixed menu for less.
- One phone lineFixed flow. Retell.
- Custom modelSelf-hosted or specific. Vapi.
- Voice mixingSeveral TTS vendors. Vapi.
- Fast to livePreset builder. Retell.
- Own infrastructureAPI-first fit. Vapi.
Both platforms sit on the same telephony and speech layers underneath. The difference is how many of those layers you are allowed to touch.
A voice agent stack we built directly
Questions people ask next
01Can you switch from Vapi to Retell later, or the other way round?
Yes, but expect a real rebuild, not a config change. The conversation logic, the tool calls and the escalation rules are written against each platform's own model. Migrating means re-testing the flow end to end, not pointing at a new API key.
02Is Vapi always more expensive than Retell?
Not always, but usually once real calls are running. Both platforms quote a low headline rate for the voice engine alone. Add the model and telephony costs and the two land in a similar range. The model you pick moves the total more than the platform does.
03Which one handles emergency or urgent calls better?
Neither platform decides that for you. The safety behaviour, detect early, say one line, transfer immediately, is something you design and test regardless of which platform runs the call. See our answer on whether an AI receptionist should handle emergency calls for the rule set.
04Do I need to be a developer to use either one?
Retell's workflow builder gets a non-technical team to a working agent for standard flows like booking and transfers. Vapi expects an engineer from the start, since custom LLMs, tool calling and voice mixing all run through its API rather than a form.
05Should we build the voice pipeline ourselves instead of using either platform?
Worth considering once volume is high enough that platform fees outweigh the cost of owning Twilio, a speech vendor and the model directly. We built that route for a client running multi-branch phone and supplier calls. The call volume and a shared dashboard across branches justified owning the stack.
