Retell AI vs Vapi vs Synthflow for Agencies (2026)
For agencies reselling AI voice agents in 2026, Retell AI has the simplest all-in pricing ($0.07 to $0.31 per minute) and a self-serve HIPAA BAA. Vapi suits developers: $0.05 per minute plus separately billed providers, with HIPAA a $2,000 per month add-on. Synthflow is now enterprise-only, from $30,000 per year.
Disclosure: Call Supplai is a white-label platform built on Retell AI, so we have a stake in this comparison. Every figure below links to the vendor’s own page, checked on September 29, 2026.
Retell AI vs Vapi vs Synthflow at a glance
Retell AI, Vapi and Synthflow differ most on pricing structure, HIPAA terms and white-label support. Synthflow also removed in-product reselling on September 15, 2026.
| Retell AI | Vapi | Synthflow | |
|---|---|---|---|
| Pricing model | Pay-as-you-go, all-in per minute | Platform fee per minute + providers billed separately + plan tiers | Enterprise contracts only |
| Published price | $0.07–$0.31 / min | $0.05 / min platform fee, plus model, voice and telephony | From $30,000 / year |
| Free credits | $10 | $5 | Not published |
| Free concurrency | 20 calls | 4 calls (Free plan) | Not published |
| HIPAA BAA | Self-serve BAA | $2,000 / month add-on | Available after agreement review |
| SOC 2 | Type 1 and Type 2 | Type II | SOC 2 (type not stated in docs) |
| White-label for agencies | Through partners such as Call Supplai | API-first; no native agency dashboard | Agency features documented; in-product reselling removed Sept 15, 2026 |
Sources: Retell AI pricing and compliance docs; Vapi pricing, HIPAA docs and trust center; Synthflow pricing, security docs and rebilling docs.
How does Retell AI pricing compare with Vapi?
Retell AI quotes one per-minute price that bundles infrastructure, voice, model and telephony, ranging from $0.07 to $0.31 per minute depending on the voice and model. Phone numbers are $2 per month. See our Retell AI pricing breakdown for a worked example.
Vapi charges a $0.05 per minute platform fee, then passes through each provider separately: speech-to-text around $0.01 per minute, OpenAI models from about $0.008 to $0.045 per minute, ElevenLabs voices from about $0.015 to $0.024 per minute, and telephony depending on the carrier. Vapi also has plan tiers: Free, Core at $29 per month, Pro with a $999 per month minimum, and custom Premier.
In practice, both land in a similar per-minute range for comparable setups. Retell AI is simpler to quote to clients; Vapi gives developers finer control over each provider.
Which platform is best for HIPAA and healthcare clients?
For agencies serving medical practices, the BAA terms differ sharply:
- Retell AI requires a signed BAA before any PHI flows through it and lets customers self-sign it. Its pricing page also lists a “custom BAA” for Enterprise.
- Vapi offers HIPAA as an add-on at $2,000 per month, including a BAA and data processing agreement.
- Synthflow offers a BAA to HIPAA customers after a separate agreement review, on enterprise contracts.
For an agency with a handful of clinics, a $2,000 per month HIPAA add-on can outweigh the entire revenue from those clients. Read what HIPAA actually requires for AI receptionists before selling to healthcare.
Which platform supports white-label reselling?
None of the three sells a turnkey white-label product for small agencies today. Retell AI works through partners, Vapi expects you to build your own layer, and Synthflow has moved agency features into enterprise contracts.
- Retell AI does not sell a white-label product itself. It runs a Certified Partner program, and agencies white-label Retell AI through partners. Call Supplai is listed in Retell AI’s partner directory.
- Vapi is API-first: you can build Vapi into your own product with no Vapi branding, but there is no native agency dashboard, so agencies either build one or use a third-party wrapper.
- Synthflow documents agency features such as sub-accounts, branding and custom domains, but it removed in-product reselling through Stripe on September 15, 2026, and its pricing is now enterprise-only.
What features do all three platforms share?
Retell AI, Vapi and Synthflow all support the core features agencies need:
- Call transfer to a human
- Outbound and batch calling campaigns
- Multiple languages
- Function calling and webhooks to connect CRMs and calendars
- Knowledge bases from documents and websites
- Post-call analysis and data extraction
The differences that matter for agencies are pricing structure, BAA terms and how white-labeling works, not the core call features.
Which AI voice platform should an agency choose in 2026?
- Choose Retell AI if you want simple per-minute pricing you can quote to clients, a self-serve HIPAA BAA, and a white-label layer through a partner such as Call Supplai.
- Choose Vapi if you have developers who want to pick every provider and build your own client-facing product.
- Choose Synthflow if you are an enterprise buyer ready for an annual contract starting at $30,000.
To see how agencies white-label Retell AI with Call Supplai for $197 per month, book a demo.
Frequently asked questions
Is Retell AI cheaper than Vapi?
For comparable setups, Retell AI and Vapi land in a similar per-minute range. Retell AI quotes one all-in price of $0.07 to $0.31 per minute; Vapi charges a $0.05 per minute platform fee plus separately billed model, voice and telephony costs. For healthcare, Vapi's $2,000 per month HIPAA add-on makes Retell AI cheaper.
Does Vapi offer a white-label agency dashboard?
No. Vapi is API-first: you can build it into your own product without Vapi branding, but it has no native agency dashboard or client sub-accounts.
Can agencies still resell Synthflow?
Synthflow removed in-product reselling through Stripe on September 15, 2026, and its pricing is now enterprise-only, starting at $30,000 per year.