Sonex Labs vs Vapi: what a voice agent really costs, and where each one fits (2026)

Why this comparison comes up

Teams that search for a Vapi alternative are usually reacting to one of three things: an invoice that came out higher than the headline rate suggested, difficulty getting numbers in their market working, or a language that their chosen speech providers handle poorly. All three come up often for teams calling into India and other multilingual markets, which is the focus here.

A phone voice agent has five cost and quality components: speech to text, the language model, text to speech, the platform that orchestrates them in real time, and the telephony that connects the call. Vendors differ mainly in which of these they bundle, which they let you swap, and who you call when one of them fails.

What are Sonex Labs and Vapi?

Sonex Labs is a voice agent platform (Sonex Flows) that bundles speech to text, text to speech and telephony on Sonex numbers into one per-minute rate: $0.055 pay as you go, or $0.050 on a $5/month plan, as listed on our pricing page. The language model is billed separately: bring your own LLM key at zero markup, or use our Vyas LLM at $0.30 per million input tokens and $0.60 per million output tokens ($0.20 and $0.40 on the monthly plan). Our text to speech covers 250+ languages, including 36+ Indian languages and dialects, and our speech to text covers 100+. Agents answer in about 300 ms end to end, and every language page under text to speech has a live playground.

Vapi is a developer platform for building voice agents, where you pick the transcriber, model and voice and Vapi runs the real-time orchestration. It charges a hosting fee of $0.05 per minute and passes provider usage through at cost, according to its pricing page (checked 2026-10-24). Its documentation lists 11 transcriber providers, and you can attach your own provider keys so that each provider bills you directly.

What should you weigh when choosing?

Five factors decide most of these evaluations. The first is the all-in cost per minute at your real volume, including telephony and the language model, because the platform fee is often less than half of the bill. The second is telephony in your market: whether you can use local numbers or your existing carrier, and whether the documented setup works with local rules, which in India affect where calls can be terminated. The third is language coverage for the languages your callers actually speak, including callers who switch languages mid-sentence. The fourth is who runs the speech stack: you, or the platform. The fifth is operational fit: concurrency, support terms, compliance documents and deployment options. Latency matters too, but vendors measure it in different ways, so it is better tested than read off a website.

Sonex Labs and Vapi at a glance

What does a minute of calling really cost?

Our rate already includes speech to text, text to speech and telephony on Sonex numbers, so the main variable left is the language model. If you bring your own telephony, no minute charge applies to it and your carrier bills you directly. Speech to text is billed by the second, as described on our pricing page.

On Vapi, the $0.05 hosting fee is one line of the bill. Its own pricing calculator shows a 1,000-minute example with Deepgram transcription at $0.0095 to $0.0099 per minute, an OpenAI model at $0.0077 to $0.0452 per minute and an ElevenLabs voice at $0.0146 to $0.0238 per minute, for an estimated $82 to $129 a month before telephony. Vapi's free numbers are US area codes only and inbound only, so outbound or international calling means paying a carrier; the pricing page lists Twilio at $0.008 per minute inbound and $0.014 outbound, Vonage at $0.00814 and Telnyx at $0.0055, without per-country rates.

The worked examples below use these assumptions. Calls are outbound and average three minutes, and every connected minute is billed. Calls run in an eight-hour window across 22 working days, which puts average concurrency near one call at 10,000 minutes and near ten at 100,000 minutes; we plan for peaks of 3 and 20 simultaneous calls. The Vapi stack uses the low end of each range in Vapi's own calculator (Deepgram $0.0095, ElevenLabs $0.0146) plus Twilio outbound at $0.014, the rate Vapi publishes. Sonex is on the $5 monthly plan, with the fee added on top of $0.050 a minute. The language model is shown separately for both, because both platforms let you bring your own key. For Vyas LLM we assume 8,000 input tokens and 200 output tokens per call minute (about four turns with a 2,000-token context), roughly $0.0017 per minute at the monthly-plan rates. Your prompt size will change that.

At 10,000 minutes a month, the bundled rate comes to about $505 against about $881 for the Vapi stack before the language model, a difference of about $375, because speech, voice and telephony are not stacked on top of the platform fee. The cost is also predictable: one rate per minute, rather than four provider rates that each move independently. At 100,000 minutes the per-minute gap is similar, and the one line to settle is concurrency. Vapi publishes its concurrency pricing and includes four calls without a package; our platform capacity is 10,000 concurrent sessions, but get your own account's limit in writing before you compare totals.

Can you call Indian numbers on your own carrier?

Sonex Labs includes telephony on Sonex numbers in the agent price, and you can bring your own telephony with no minute charge from us, so you can keep the numbers and carrier contracts you already have. Indian outbound calling comes with rules on calling hours, consent and caller identity, which we cover in our article on TRAI robocall rules. Sonex outbound campaigns take calling windows, time zones and retry limits, so calls go out only in the hours you set and stop after the number of attempts you choose.

On Vapi, the Plivo integration guide states that Indian phone numbers cannot be used with Plivo on Vapi because TRAI regulations require SIP termination on an Indian server that Vapi does not currently support. Vapi's outbound calling docs describe importing numbers from Twilio, Vonage or Telnyx. We could not find Vapi documentation for an Indian Exotel setup, so as of 24 October 2026 we would describe it as not documented rather than unsupported.

Which speaks your customers' languages?

We publish one list: 250+ languages for text to speech, including 36+ Indian languages and dialects such as Bhojpuri, Marwari, Garhwali and Maithili, and 100+ for speech to text, at one rate per language. You can hear any language before building, on its live playground under text to speech. Pāṇini reads mixed text such as Hinglish naturally in one voice, and Valmiki detects the spoken language automatically, which helps with callers who switch languages. For an agent that calls in Hindi, Tamil, Telugu and Bengali, that is one configuration rather than several provider evaluations.

On Vapi, language support depends on the providers you choose. Its Deepgram page lists Hindi, Bangla, Kannada, Marathi, Tamil, Telugu, Urdu and Indian English on Nova 3, a multilingual mode for code-switching callers, and Hindi as the only Indian language on the Flux multilingual model. Other transcribers and voices on Vapi's list have their own coverage, so each combination needs its own research and testing.

Who runs the speech stack, you or the platform?

On Sonex Labs we run the speech and voice models, Pāṇini and Valmiki, and you configure the agent and choose its language model; the developer docs cover the API. Agents can transfer a live call to a human agent, call your tools during the conversation, including over MCP, and connect to HubSpot, Salesforce, n8n, Zapier and Make; calls can be recorded and transcribed. Your engineers spend their time on the agent's behaviour and integrations rather than on keeping a speech pipeline working.

Vapi lets developers swap transcribers, point the agent at a custom LLM endpoint and choose among several warm transfer modes, with tools covering server functions, API requests, assistant handoffs, knowledge bases and MCP. That provider-level control is its main advantage for teams that already hold negotiated speech contracts or a fine-tuned model.

What do you get on latency, scale and support?

We publish about 300 ms end to end, from when the caller stops speaking to when the agent starts, and Vapi's homepage reports average latency below 500 ms. Both are vendor-reported and measured differently, so measure on your own calls. Our platform capacity is 10,000 concurrent sessions; ask for your account's limit before a large campaign.

Vapi's pricing page publishes support and uptime SLAs by tier (up to 99.9% with a one-hour P0 response on Premier) and a HIPAA add-on at $2,000 a month with a BAA. If a written SLA, SOC 2 report or BAA is a hard requirement, ask each vendor for the documents and compare them side by side.

When is Sonex Labs the better choice?

Choose Sonex Labs if you run collections, EMI reminders or renewal calls in regional languages, where the caller needs to hear Hindi, Tamil, Telugu, Marathi or Bengali, or a dialect such as Bhojpuri or Marwari, without assembling a provider for each. Choose it if your numbers already live with a carrier: bring your own telephony and pay no minute charge to us for it.

Choose it if you want predictable cost at volume, with speech, voice and telephony in one rate, about $505 for 10,000 minutes in the worked example above, and the language model on your own key at zero markup or on Vyas LLM. Choose it if you want campaign calling windows, retry limits, live transfer to your team, recordings and transcripts, and CRM connectors on the platform rather than built yourself. If you expect many simultaneous calls, get your account's concurrency limit in writing up front.

When is Vapi the better choice?

Choose Vapi if your engineers want to pick and maintain each speech, voice and model provider themselves, for example because you already have negotiated rates or a fine-tuned model behind your own endpoint, and you mainly call US numbers. It also fits if you need published concurrency pricing, its published uptime SLAs or its HIPAA add-on today, or tools such as warm transfer modes and MCP documented in detail.

How to test both before you commit

Build the same agent on both platforms with the same prompt, the same tools and, where possible, the same language model on your own key, so the model is not the variable. Use the telephony you would use in production: a local Indian number if you call India, not a US test number. Place at least 50 calls per platform from real mobile phones across your languages, including callers who mix them. Measure latency at the handset, from the end of the caller's speech to the start of the reply. Score each call on names, phone numbers, dates and amounts, where recognition errors cost most. Then compare a week of real invoices, including concurrency charges, against the worked examples above.