Smallest.ai vs Sonex Labs: languages, accuracy evidence and real monthly cost (2026)

Why compare Smallest.ai and Sonex Labs?

Smallest.ai and Sonex Labs are often shortlisted together because both sell the whole voice stack rather than one piece of it. Each has its own text-to-speech model, its own speech-to-text model and a platform for building phone agents on top of them, and both pay attention to Indian languages. The headline claims sound similar, so the decision comes down to details: which languages each covers in each direction, what a minute of agent time costs once every component is counted, and how many calls you can run before you have to talk to sales.

Smallest.ai's documentation pages sometimes disagree with one another on language counts. Where a figure is not published, or where its pages conflict, we say so rather than guess, and every Smallest figure below links to the page it came from.

What are Sonex Labs and Smallest.ai?

Sonex Labs is a voice platform built around the languages most speech APIs cover thinly. Pāṇini, our text-to-speech model, speaks more than 250 languages in 34 writing systems, including 36+ Indian languages and dialects (languages). Valmiki, our speech-to-text model, covers more than 100 languages (speech to text). Our voice agents combine both with telephony on Sonex numbers and a language model you choose, at a single per-minute rate (pricing).

Smallest.ai is a voice AI company that offers Lightning text to speech, Pulse speech to text, a full-duplex speech-to-speech model called Hydra, and its own Electron language model (Smallest models overview, checked 24 October 2026), plus a hosted voice agent platform, Atoms (Smallest pricing). Agents are charged per minute depending on the models you select, and the platform lists separate per-minute prices for hosting, transcription, speech and add-ons (Smallest pricing).

What should you weigh when choosing?

Start with language coverage, checked separately for listening and speaking. A product can transcribe a language it cannot speak, and a voice list can include a language only by routing it through another language's voices. Then listen to how each sounds on a phone line, and measure latency at the caller's ear, including the phone network. Third is the full per-minute cost of an agent call, adding up hosting, transcription, the language model, speech and telephony, rather than one headline rate. Fourth is capacity: how many calls you can run at once on self-serve terms. Fifth is where the system can run if your data must stay in your own cloud. Last is the platform around the agent, meaning carriers, call records and add-ons, which decides how much you build yourself.

Sonex Labs and Smallest.ai at a glance

Which can both listen and speak in your customers' languages?

Pāṇini speaks more than 250 languages across 34 writing systems, and its 36+ Indian languages and dialects go below state languages to Bhojpuri, Marwari, Haryanvi, Chhattisgarhi, Mewari, Garhwali, Maithili, Saraiki, Braj, Bundeli, Angika and Bhili (languages). Outside India it covers Arabic in Modern Standard Arabic and nine dialects: Gulf, Egyptian, Levantine, Najdi, Iraqi, Moroccan, Algerian, Tunisian and Sudanese. Every language page has a live playground, and every language costs the same per character (text to speech).

Pāṇini has 120 platform voices and clones a voice from a 10-second sample, and a voice or clone can speak across languages (text to speech). It reads mixed-language text such as Hinglish naturally in one voice. Valmiki transcribes more than 100 languages and detects the spoken language automatically (speech to text). Check each language and dialect you need in both directions, including the way your callers mix languages.

Smallest's standard voice model, Lightning v3.1, has voices in 12 languages: English, Hindi, Tamil, Spanish, Kannada, Marathi, Telugu, Odia, Punjabi, Malayalam, Gujarati and Bengali (Smallest voices and languages). Its overview page lists 20 accepted language codes and says those without voices are routed through English or Hindi voices (Lightning overview); a changelog entry (dated May 2026 in its URL) corrected the list to the 12 languages with voices in the catalog (changelog). Lightning v3.1 Pro adds languages including Arabic, Mandarin, Japanese, Korean and Turkish, with 31 on the models page and 29 on the voices page. On transcription, Pulse lists 21 streaming languages, including Hindi, Gujarati, Marathi, Odia, Bengali, Tamil, Telugu, Kannada and Malayalam; the four south Indian languages are India-region only and marked Beta, and for pre-recorded files Hindi is the only single Indian language listed (Pulse overview).

How do they sound and respond on a real phone call?

Pāṇini is trained for 8 kHz phone audio and starts streaming audio in under 200 milliseconds (time to first byte), and Sonex voice agents answer in about 300 milliseconds end to end, from when the caller stops speaking to when the agent starts (text to speech). Smallest gives 200 milliseconds to first byte for Lightning (models overview), with native 44.1 kHz output, configurable sample rates from 8 kHz to 44 kHz and μ-law encoding (Lightning overview); we did not find an end-to-end response figure for Atoms. All of these are vendor-reported, so measure at the caller's end.

On accuracy, Smallest has published more. It reports that Pulse Pro, its English batch model, averages a 5.42% word error rate on the ESB benchmark, tied second on the public Open ASR Leaderboard (Pulse overview); we found no published figure for Indian languages or streaming. Sonex Labs has not published a WER or MOS benchmark, so the test plan at the end of this article is the way to compare both on your own calls.

What does a full voice pipeline cost per month?

Sonex Labs charges $0.055 a minute for voice agents on pay as you go, including speech to text, text to speech and telephony on Sonex numbers; bring your own telephony and no minute charge applies to it. You bring your own LLM key at zero markup or use our Vyas LLM. Standalone, Valmiki is $0.00525 per minute of audio, billed by the second, and Pāṇini is $0.03125 per 1,000 characters, or $0.028125 on the $5 a month plan, at the same rate in every language. The free tier is 10,000 characters and one voice clone, no card required (pricing, checked 24 October 2026).

Smallest lists agents at $0.09 to $0.21 a minute on pay as you go, depending on the models selected, and from $0.05 a minute on Enterprise (Smallest pricing, checked 24 October 2026). Its components are $0.01 a minute for hosting, about $0.009 for speech to text, about $0.09 for text to speech, language models at cost (for example $0.045 a minute for GPT-4.1), and telephony at cost through an external or bring-your-own carrier. Phone numbers are $10 a month each, and new accounts get $10 of credit. The page gives no per-character speech price, only the approximate per-minute figure.

The examples below use pay-as-you-go list prices and three-minute agent calls. The agent rows leave the language model out of both sides, since you can run the same model on either; the Smallest figure is its hosting, transcription and speech components, $0.109 a minute, before telephony. Because Smallest prices speech per minute and we price it per character, we convert at an assumed 900 characters per spoken minute, about 150 words. Character counts vary by script, so check this against your own scripts.

On published pay-as-you-go prices, Sonex is lower in each scenario, and the gap is largest in speech generation, where Smallest's approximate $0.09 a minute compares with roughly $0.028 at our per-character rate under the stated assumption. Capacity affects cost too: Smallest's pay-as-you-go plan includes a published 20 concurrent calls and sells more only on Enterprise, while we list platform capacity rather than a per-account figure, so ask both vendors for your account's limit before a busy outbound campaign.

Which is built for running phone calls at volume?

The Sonex agent price includes telephony on Sonex numbers, so calls run without a separate carrier account, and you can still bring your own telephony with no minute charge from us. Platform capacity is 10,000 concurrent sessions (pricing). Agents can transfer a live call to a human agent, use MCP and tool calling, and connect to HubSpot, Salesforce, n8n, Zapier and Make. Calls can be recorded and transcribed, and outbound campaigns take calling windows, time zones and retry limits.

Smallest's Atoms platform lists a knowledge base at $3 per GB per user plus $2 per 1,000 queries, PII removal at $0.01 a minute, post-call analytics and a HIPAA zero-data-retention option at $1,000 a month as add-ons, and its Enterprise package states a 99.99% uptime SLA, on-premise deployment, SSO, SOC 2 support and forward-deployed engineers (Smallest pricing). Its SIP trunking guide walks through Twilio, Telnyx and Vonage, names Bandwidth and Plivo, and covers self-hosted Asterisk, FreeSWITCH and Kamailio (SIP trunking).

When is Sonex Labs the better choice?

Sonex Labs is the better choice when your callers speak languages or dialects outside Smallest's voice list. Pāṇini covers Bhojpuri, Marwari, Haryanvi, Chhattisgarhi, Garhwali, Maithili, Bundeli, Braj, Angika and Bhili, nine Arabic dialects as well as Modern Standard Arabic, and the rest of a 250+ language list, all at the same per-character price as English (languages, pricing).

It suits teams that want one provider and one price for the whole call. At $0.055 a minute including speech to text, text to speech and telephony on Sonex numbers, with your own LLM key at zero markup or our Vyas LLM, the monthly bill is a single rate rather than a sum of components plus carrier charges. Live transfer, MCP and tool calling, CRM connectors, recordings and transcripts, and campaign calling windows and retries are part of the same platform. On published pay-as-you-go prices, our speech generation also costs about a third of Smallest's per spoken minute, under the stated assumption (pricing).

When is Smallest.ai the better choice?

Smallest.ai is the better choice when your audio is English-heavy, your Indian-language needs fall within its 12 Lightning v3.1 voice languages, you need 20 concurrent calls on self-serve terms at a published price, you want a published English transcription benchmark, and you want packaged add-ons such as a knowledge base and PII removal, or a speech-to-speech architecture through Hydra, without building them yourself. Its 44.1 kHz output also suits teams that will reuse the same voices in apps or media, and its Enterprise package, with a stated 99.99% uptime SLA and forward-deployed engineers, suits buyers who want hands-on help at contract time. Teams that already run their own carrier will find its SIP trunking guide covers the major providers and self-hosted switches.

How should you test both before deciding?

Neither vendor has published accuracy figures for Indian-language phone audio that you can rely on for your use case, so test on your own. Gather fifty to a hundred real call recordings per language, including noisy lines and callers who mix languages, and have native speakers write reference transcripts. Run them through Pulse and Valmiki and score the error rate separately for names, numbers, amounts, dates and addresses, because those are the errors that break a booking or a payment.

For voices, write one script per language containing the same hard items and have native listeners rate each provider blind over a phone line. For agents, place at least twenty calls per configuration over the same carrier and time the gap from the caller's last word to the first audible reply, measured at the caller's end. Smallest's $10 credit and our 10,000 free characters cover a first round.