Vapi vs Retell AI: build your own stack or run a managed studio?

Who's going to maintain the agent once it's live?

That's the question that settles this pair faster than any feature list. A voice agent isn't a one-off build. Someone has to tweak the script when callers get confused, swap a voice that sounds wrong, add a transfer rule when a new team joins, and check what went badly on last week's calls. If that person is an engineer who lives in a code editor, you'll lean one way. If it's an operations lead, a practice manager or a sales team, you'll lean the other.

Where something below is the vendor's own claim, it's labelled as one, so you can see what's a promise and what's a plain product detail.

The plumbing is shared, the philosophy isn't

Here's something that surprises people. The phone side of both products leans on the same carriers. Vapi's docs list Twilio, Telnyx, DIDWW and SIP trunking as ways to connect numbers, and Retell's home page lists Twilio and Vonage, with docs covering number purchase, custom telephony over SIP and branded caller ID. So the call itself travels over familiar pipes either way. The carrier isn't what you're choosing.

What you're choosing is how much of the stack you want in your hands. The developer platform hands you each piece separately: speech-to-text, the language model and text-to-speech, picked from dozens of providers such as OpenAI, Anthropic, Google, Deepgram and ElevenLabs, or set with one-click presets if you don't want to choose. The other product sells a managed flow instead, framed around industries and use cases, with a no-code studio and an AI building assistant called Conductor.

There's one more thing worth knowing. A common shorthand used to be that one of these was only for prototypes. That gap doesn't show on either site any more. Both now talk about testing before launch and watching agents once they're running, so don't pick on that old assumption.

My advice before you read the detail

If you've got developers who want control over every component and want the agent's setup versioned in git alongside the rest of your code, start with Vapi. If you want a phone agent running for a business team quickly, starting from receptionist, lead qualification or collections style use cases, start with Retell AI. Neither site gives grounds for calling an overall winner. It comes down to control versus a faster managed path, and who on your side will own the thing.

Side by side on the seven differences that matter

Area	Vapi	Retell AI
How you build	Developer platform: single Assistants and multi-assistant Squads, a CLI and config as code in git	Single prompt, conversation flow and multi-prompt (legacy) agent types, no-code studio, Conductor AI assistant
AI components	Pick speech-to-text, model and voice separately from dozens of providers, or use presets	Language, voice and speech settings plus an LLM playground; no comparable provider catalogue seen
Phone connections	Twilio, Telnyx, DIDWW, SIP trunking, plus a free number	Twilio and Vonage listed; buy numbers, custom SIP, branded caller ID
Outbound and testing	Campaigns and Simulations for testing before customers call	Batch calling, a dialer, verified numbers to avoid spam flags, AI quality assurance
Who the home page speaks to	Builders, with Fortune 100 scale, support SLAs and an embedded engineer	Industries such as healthcare, finance, insurance, logistics, retail, travel and debt collection
Compliance	Vendor claim: SOC 2, HIPAA and PCI compliant, with guardrails against hallucination	Links a Trust Center describing its security and compliance approach
Chat and SMS	Voice first; inbound SMS sits under phone numbers	Chat agents, a website widget and two-way SMS from one build

Grouping the gaps by what you'll feel day to day

Building and changing the agent

The builder-first option gives you two primitives. An Assistant handles a single conversation, and a Squad links several assistants together so one can hand off to another. There's a CLI, and the docs push config as code, which means changes can go through the same review process your developers already use. That's lovely if you've got that process. It's a hurdle if you don't.

The studio option offers three agent types: single prompt, conversation flow and an older multi-prompt type the docs mark as legacy. The vendor says the no-code studio lets your own team run it without relying on the company for every change, and Conductor is there to help you build. If the person editing the agent isn't technical, that's the side to look at first.

Voices, models and how much you can swap

This is where the developer platform pulls clearly ahead on choice. You can mix a transcriber from one provider, a model from another and a voice from a third. The vendor also claims sub-600ms response times, which is its own number. The studio's docs cover language, voice and speech settings and an LLM playground, but its site doesn't show the same wide catalogue of providers. If swapping components matters to you, ask before you commit.

Outbound calling and quality checks

If your agent mostly dials out, the studio product shows more on the page. Its product menu lists batch calling, a dialer, verified phone numbers to help avoid spam flags and AI quality assurance. The developer platform's docs mention campaigns and Simulations, which let you rehearse calls before real customers ring. Both cover the basics, but one puts outbound tooling front and centre.

Beyond the phone line

Want the same agent on your website chat and over text? The studio's docs cover chat agents, a website widget and sending and receiving SMS, so one build can span voice and chat. The other platform's docs stay focused on voice, with inbound SMS covered under phone numbers. If you need several channels from one place, that tips things.

Where each one could let you down

• The developer platform: all that choice means someone has to make the choices. Without a technical owner, you'll be stuck with presets or waiting on a developer for every change.
• The studio: its site doesn't state much detail on how its agent types differ, and it doesn't show a wide provider catalogue. If you want to bring a specific model or voice, check first.
• Both: compliance wording comes from the vendors. One claims SOC 2, HIPAA and PCI; the other points to its Trust Center. If you're in a regulated sector, read the documents yourself rather than relying on a home page line.

If neither fits the shape of your team, our roundup of the voice agent platforms worth shortlisting covers the wider field, and if all you need is someone answering the phone, the guide to the best AI receptionist tools is the quicker read.

Four more names to put beside them

Bland AI

Best for: Enterprise phone agents also deployed on SMS and web; the vendor says it's built for regulated, high-stakes calls in healthcare, insurance and financial services.

Synthflow

Best for: Contact centres, BPOs and multi-location brands wanting agents that answer and make calls inside their existing phone system and update the CRM mid-call.

ElevenLabs Agents

Best for: Teams that care most about voice quality and language range; the vendor claims low latency conversations in dozens of languages.

Voiceflow

Best for: Customer service teams building chat and voice agents together in a shared Studio, with Rehearsal to simulate conversations before launch.

Do you make AI voice agent software? Tool makers can ask to be considered for a featured place on this page.

Running a bigger support operation? The list of AI call centre software goes further on that side.

Three questions to settle with your team first

1. Who will edit the agent after launch, an engineer or someone in operations?
2. Are most of your calls inbound, like a receptionist, or outbound, like reminders and lead follow-up?
3. Do you need chat and text from the same build, or is voice enough for now?

Write your answers down before any sales call. If an engineer owns it, your calls are mostly inbound or custom, and voice is enough, you're looking at the builder's platform. If it's an ops lead, you dial out a lot and you want chat too, the studio is the more natural fit.

Want your tool on this list? Featured spots and reviews here are paid partnerships. Here's how to partner with me.

Frequently asked questions

Is Vapi or Retell AI easier for a non-technical team?

The studio is the easier starting point for non-technical teams. Its no-code studio and Conductor assistant are built so your own staff can make changes, while the other is framed as a developer platform with a CLI and config as code.

Can I choose my own AI model and voice?

On the developer platform, yes: you pick speech-to-text, the model and the voice separately from dozens of providers. The studio's docs cover voice and speech settings and an LLM playground, but its site doesn't show the same wide choice, so ask before you sign up.

Do both work with Twilio?

Yes. Both list Twilio. The developer platform also lists Telnyx, DIDWW and SIP trunking, and the studio lists Vonage, custom SIP and branded caller ID.

Which is better for outbound calling campaigns?

The studio product shows more outbound tooling on its site: batch calling, a dialer, verified numbers to avoid spam flags and AI quality checks. The developer platform mentions campaigns and Simulations for testing.

Is there a free trial?

Retell's site states a free trial. The developer platform's site doesn't state a free plan.