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Comparison
Knock Knock vs. Retell AI and Vapi
Retell and Vapi are excellent at what they are: infrastructure for developers building voice agents. Neither ships a native white-label layer an agency can resell. That is not a flaw in their products — it is a different product category, and it is the whole comparison.
Retell and Vapi pricing, docs and 2026 changelogs verified on 11 September 2026. Knock Knock pricing and tier features read from knockknockapp.ai/pricing on 11 September 2026.
The honest framing: this is build versus buy
Retell and Vapi are genuinely strong platforms. Retell publishes a rate for every component of a call — infrastructure, speech, model, telephony — so your cost is predictable if you are willing to do the arithmetic. Vapi charges $0.05/min for its own orchestration and passes model, speech and telephony costs through at cost. Both give a developer enormous control.
What neither gives you is a product to sell. As of September 2026 neither has a native white-label or reseller layer: no client-facing branded portal, no per-client rebilling with your margin on it, no way to remove their brand from something your client logs into. Vapi has Organizations, which separates workspaces per client — useful, but it is workspace isolation, not a reseller layer. Nothing your client sees is yours.
One correction worth making, because it is often stated wrongly: these are no longer voice-only. Retell sells voice, chat and SMS with published per-message pricing, and Vapi has shipped a Chat API and SMS. If a comparison tells you they only do voice, it is out of date.
Side by side
| Retell AI / Vapi | Knock Knock | |
|---|---|---|
| Product category | Developer infrastructure. Retell: “AI voice agent platform for automating phone calls.” Vapi: “voice agents for builders” | A finished agency product, sold by sub-account and resold under your brand |
| Native white-label | Neither offers one. Retell maintains a directory of third-party white-label vendors; Vapi’s Organizations isolate workspaces but expose nothing brandable to the client | Built in — white-label plus a custom domain from the $275 Startup tier upward |
| Client rebilling | You build it. Both bill you; per-tenant metering, margin and invoicing are yours to implement | Sub-accounts are part of the plan; you price your clients however you choose |
| Pricing | Retell $0.07–$0.31/min itemised by component, plus $2/mo per number. Vapi $0.05/min for orchestration plus model, speech and telephony at cost | $197 / $275 / $599 / $1,197 per month, each with a monthly AI wallet covering all usage |
| Cost predictability | Retell: good — every layer has a published rate. Vapi: hard to forecast, because the other layers are whatever your chosen providers charge | One monthly figure plus a wallet you can top up |
| Channels | Retell: voice, chat, SMS, API. Vapi: voice, chat, SMS (SMS must be started by the customer) | Voice, chat, live video, plus SMS and WhatsApp through GoHighLevel |
| Visitor identification | Neither | KnockID identifies anonymous traffic as named CRM leads |
| Live session view | Neither. Both record calls, which is not the same thing | Yes — live website session visibility |
| CRM | Retell ships a built-in CRM with Salesforce and HubSpot sync; Vapi integrates via API | GoHighLevel native, plus HubSpot |
We have not published an all-in per-minute figure for Vapi. Their model makes it genuinely unknowable in advance, and any single number would be invented.
What an agency actually has to build on top
This is the part that does not show up on a pricing page. To resell a branded voice product on either platform, you build or buy all of the following:
- Multi-tenant isolation. Retell has no sub-account primitive at all. Vapi has Organizations, but creating them programmatically is not publicly documented, so onboarding likely involves a manual step.
- A client-facing branded portal. Call logs, transcripts, recordings, analytics — the entire surface your client sees. Neither vendor exposes anything rebrandable.
- Billing, metering and margin. Both bill you at cost. Per-tenant usage metering, your markup, subscriptions, invoicing and overages are yours. This is the largest item and the one most often underestimated.
- Authentication and roles. Signup, login, resets, per-client permissions, and key custody so a client never touches your master API key.
- Agent provisioning. Cloning a working configuration to a new tenant with its own prompts, voices, numbers and knowledge bases.
- Phone number lifecycle per tenant, including 10DLC registration if you use SMS.
- Support and observability you own. To your client, you are the vendor.
The alternative is a third-party wrapper — which means a second vendor, a second subscription and a second point of failure between you and your clients, with your billing layer owned by somebody else.
Which one you should actually pick
Choose Retell or Vapi if…
- You have engineering capacity and want total control over the agent stack.
- You are building a product of your own, not reselling someone else's.
- You need to swap models, voices or providers freely — this is exactly what they are for.
- Your use case is a single deep voice integration rather than many client accounts.
Choose Knock Knock if…
- You want to sell to clients next month, not after a build cycle.
- White-label, custom domain and sub-accounts need to be in the product rather than on your roadmap.
- You want one bill you can mark up, not a stack of provider invoices to reconcile.
- Visitor identification, live session view, chat and video matter as much as the phone call.
Frequently asked questions
Do Retell or Vapi offer white-labelling?
Not natively, as of September 2026. Retell runs a partner directory listing third-party white-label vendors, which is itself a strong signal that it is not a native capability. Vapi offers Organizations, which separate workspaces per client but provide no branded client portal, no brand removal and no rebilling.
Isn't Vapi's Organizations feature the same as sub-accounts?
Not quite. Organizations give each client isolated assistants, numbers, knowledge bases and logs, which is real and useful. What they do not give you is anything the client sees with your name on it, or any mechanism to bill them with your margin applied.
Are Retell and Vapi voice-only?
No, not any more. Retell sells voice, chat and SMS with published per-message pricing, and Vapi has shipped a Chat API and SMS chat. Voice remains the centre of gravity for both, but a comparison claiming they are voice-only is out of date.
Which is cheaper?
It depends on what you count. Retell's itemised rates land a typical configuration around $0.165/min all-in, and every component is published. Vapi charges $0.05/min for its own layer and passes the rest through at cost, so the total depends on your providers. Neither figure includes the cost of building the reseller layer, which is the expense that actually decides this comparison.
Can I use Retell or Vapi and still white-label it?
Yes, by building the layer yourself or by paying a third-party wrapper vendor. Both are legitimate routes. The trade-off is engineering time and ongoing ownership in the first case, and an extra vendor sitting between you and your clients' billing in the second.
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