Speech-to-text API for AI voice agents

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Why Soniox is the best speech-to-text API for voice agents

“Best” for voice agents isn’t just about top benchmark scores on clean audio, it’s about predictable, reliable behavior in real production systems.

A speech-to-text system for voice agents should:

Deliver highly accurate transcription that keeps up with live conversation.
Run with ultra-low latency, enabling real-time LLM processing and fast responses.
Reliably detect end-of-turn speech so agents respond at the right moment.
Perform in real-world conditions with noise, accents, interruptions, and multilingual speech.
Scale economically, with pricing that works for high-volume deployments.

Soniox is built around these requirements from the ground up, delivering fast, reliable speech recognition for voice agents across 60+ languages. One unified model supports true multilingual and language-switching speech, without changing configurations, switching models, or restarting streams.

And with real-time transcription starting at ~$0.12 per hour, Soniox makes it practical and cost-effective to deploy voice agents at massive scale in any language, anywhere.

“It just gets the words right — any language, any accent, any context. That’s what accuracy is supposed to look like.”

Tony Wang,
Cofounder & Chief Revenue Officer at Agora

Lowest-latency speech-to-text in practice

Low latency in voice agents isn’t achieved through a single optimization. It’s the result of an end-to-end system: streaming audio, real-time decoding, turn detection, and fast transcript delivery, working together so agents can respond naturally without waiting for full utterances.

The Soniox API is built for this. Developers can configure transcription behavior to match their agent’s requirements, balancing responsiveness, accuracy, and conversational timing in production.

Real-time streaming transcription & translation

At the core of Soniox is a real-time speech engine designed for continuous conversational streams, not offline batch processing.

Audio is streamed over a persistent connection, and transcripts are returned immediately as speech arrives. This enables voice agents and downstream LLM systems to begin reasoning and responding in real time, without waiting for the user to finish speaking.

chevron_rightLearn about real-time transcription & translation

Endpoint detection for conversational turn-taking

Knowing when a user has finished speaking is just as important as knowing what they said.

Soniox includes built-in endpoint detection that identifies speech boundaries in real time and emits reliable end-of-turn events. Voice agents can use these signals to respond at the right moment without depending on fragile client-side silence timers.

The result is smoother turn-taking, fewer interruptions, and faster, more natural conversations.

chevron_rightUnderstand endpoint detection

Custom vocabulary without fine-tuning

Low latency alone isn’t enough if transcription errors force users to repeat themselves.

Soniox supports request-time context feature, allowing developers to inject domain-specific vocabulary, such as product names, jargon, entities, or topic knowledge, directly into the transcription stream.

This improves accuracy through simple configuration, without maintaining separate fine-tuned models for every agent or use case.

chevron_rightRead more about context customization

Speaker-native accuracy across 60+ languages

Voice agents often need to handle multilingual users seamlessly without restarting sessions or switching models mid-conversation.

Soniox provides accurate transcription across 60+ languages using a single unified multilingual model. Language identification happens automatically within the same stream, enabling agents to support bilingual and code-switched speech without reconnecting or reconfiguring the pipeline.

The result is stable latency and dramatically simpler production deployments across global languages.

chevron_rightSee the full list of supported languages

Data residency for industry compliance

For many production voice agents, data residency isn’t optional, it’s a compliance requirement. Regulated industries such as healthcare, legal, finance, and enterprise environments often require that speech and transcript data remain within specific geographic regions.

Soniox supports regional data residency, allowing voice agents to operate in regulated deployments while keeping customer data within required boundaries, all through the same real-time API.

chevron_rightGet more details about data residency

Putting it all together

Voice agents demand more than high benchmark accuracy. They require speech recognition that is fast, predictable, multilingual, and reliable in real-world production conditions.

Soniox brings these capabilities together in a single real-time API: ultra-low latency streaming, built-in turn detection, context control, speaker-native accuracy across 60+ languages, and regional data residency for regulated deployments.

If you're building voice agents that need to work globally at scale, Soniox is the speech layer designed for production.

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For voice agents that understand

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Smart voice assistants

Deliver fast, natural voice interactions inside your product to help answer questions, find information, and complete tasks.

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Support agents

Understand customers instantly across 60+ languages — without switching models — to resolve issues faster.

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In-app voice agents

Embed natural voice automation directly into your app, from onboarding and scheduling to self-service, with fast, reliable, structured responses.

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Call routing agents

Detect intent in real time and route callers instantly, even before they finish speaking. No phone menus required.

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Privacy and compliance, built right in

Never stored, never saved.

Audio stays in memory, everything is processed in real-time.

Built for privacy-critical use cases.

SOC 2 Type II–certified and HIPAA-ready from day one.

Trusted where privacy matters most.

Used in industries where speech is sensitive — from healthcare to enterprise.

SOC 2 Type 2 compliant

HIPAA compliant

GDPR compliant

Power up your multilingual AI voice agent

Get production-ready speech-to-text transcription and translation in 60+ languages.

Frequently asked questions about Soniox for voice agents

What is the Soniox Speech-to-Text API?arrow_downward

Soniox provides a real-time speech-to-text API designed for AI voice agents. It converts live audio into text with low latency, supports streaming use cases, and works across more than 60 languages without switching models or restarting the stream.

Is Soniox suitable for building AI voice agents?arrow_downward

Yes. Soniox is designed for real-time voice agent workflows, including streaming transcription, early token delivery, endpoint detection for turn-taking, all configurable through the API.

What makes Soniox a low-latency speech-to-text API?arrow_downward

Soniox uses a real-time streaming architecture that emits transcription results incrementally as audio arrives. This allows voice agents to begin processing speech before an utterance is complete, reducing end-to-end response time.

How does Soniox handle partial and final transcripts?arrow_downward

The streaming API provides non-final transcription tokens followed by finalized tokens. This enables early intent detection, real-time UI updates, and stable downstream processing without parsing entire transcripts.

How does Soniox detect when a user finishes speaking?arrow_downward

Soniox includes built-in endpoint detection that identifies speech boundaries. Voice agents can use these events to decide when to respond without relying on client-side silence timers.

Can I customize transcription behavior for my voice agent?arrow_downward

Yes. The Soniox API is configurable, allowing developers to adjust transcription behavior, including custom context for domain-specific vocabulary, eliminating the need to maintain separate fine-tuned models for different tasks.

Does Soniox support multilingual voice agents?arrow_downward

Yes. Soniox supports consistent multilingual transcription and translation across more than 60 languages using a single real-time model. Language identification happens automatically within the same stream.

Can Soniox handle language switching within a conversation?arrow_downward

Yes. Soniox can recognize and transcribe speech when speakers switch languages mid-sentence or mid-conversation, without requiring stream restarts or language-specific routing.

Is Soniox suitable for regulated industries?arrow_downward

Yes. Soniox supports data residency for regulated environments such as medical and legal use cases, allowing speech and transcript data to remain within required geographic regions while using the same real-time API.

Is audio stored when using the Soniox API?arrow_downward

No. Audio is processed in real time and kept in memory only. Soniox is designed for privacy-critical applications where speech data should not be stored by default.

How do developers get started with Soniox?arrow_downward

Developers can generate an API key on Soniox Console and start streaming audio over websockets to Soniox directly. The API integrates with common voice agent frameworks and real-time media pipelines, making it easy to add speech-to-text to existing systems.