Power best in class voice agents

Ultra-fast and ultra-accurate streaming STT built for voice agents. Get 300ms immutable transcripts and intelligent endpointing.

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Two solutions

Pick the API that fits your build

Different architectures, different tradeoffs. Both powered by industry-leading speech models.

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Voice Agent API

Our proprietary voice stack, built on Universal-3.5 Pro, via one WebSocket. Connect, stream audio in, get audio back - we handle the rest.

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$4.50 /hr

Speech, LLM, and voice all included

Best-in-class voice agents - the preferred way to build with AssemblyAI
Customer support agents, AI companions, clinical intake, language learning
Teams shipping fast - working agent in an afternoon, no infra to manage
Claude Code compatible - paste the docs and build anything

Bring your own stack

Universal-3.5 Pro Realtime

The STT layer for your cascading voice-agent architecture. Works natively with your preferred orchestrator, with Sync Speech-to-Text available for finished utterances.

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$0.45 /hr

Transcription only, unlimited concurrent streams

Teams already using LiveKit, Pipecat, or Vapi as their orchestration layer
Teams running cascading architectures: STT -> LLM -> TTS
High-scale deployments where margin and full control matter
Complex workflows with RAG, custom tooling, or proprietary LLMs
HIPAA, SOC 2 - bring your own compliance infrastructure
Sync Speech-to-Text API for teams running their own VAD and turn detection

Start building

Explore our comprehensive docs with integration guides and best practices to optimize accuracy and latency for your application.

Read the docs

Choose based on your architecture

Voice Agent API

AssemblyAI's proprietary voice stack

Universal-3.5 Pro Realtime API

Best-in-class STT for your stack

Industry-leading speech models

Unlimited concurrency

Enterprise grade reliability

Session-based pricing

Setup time

Working agent in an afternoon

Minutes to swap STT in an existing stack

Architecture

1 WebSocket · JSON messages · No frameworks required

Cascading (STT → LLM → TTS) — you own the full pipeline

LLM

Managed — update system prompt mid-conversation

Bring your own

Voice (TTS)

Included — select from natural-sounding voices

Bring your own

Pricing

$4.50/hr all-in — no token math across three invoices

$0.45/hr — STT only, unlimited concurrent streams

Integrations

LiveKit, Pipecat, any WebSocket client, Claude Code

LiveKit, Pipecat, custom WebSocket, Twilio SIP

Session resume

30-second reconnect window, context preserved

Via your orchestrator

Integrations

Ready to plug into your voice-agent stack

Pre-built integrations with step-by-step docs enabling quick implementation without disrupting existing workflows.

Join 200K+ developers building new experiences with voice data

If you have an hour of content, the difference between 99% accuracy and 97% accuracy, it's a lot of time for that person to review. So you could cut down their workflow from taking half an hour, to 20 minutes, to 15 minutes — it's huge, right?

Joshua Grossberg

CTO, Kapwing

Investments in STT improvements always pay for themselves, since it is such a critical building block of the voice pipeline.

Lindsay Liu

Co-Founder & CEO, Super

AssemblyAI's managed API endpoint and diarization won me over — something Whisper couldn't provide.

Josh Mohrer

Founder, Wave.co

We needed a provider that could scale with us — offering unlimited concurrent streams, fair pricing, and responsive support.

Mark Barbir

CEO, Earmark

The transcription accuracy, reliability, and speed of AssemblyAI's API have greatly enhanced our operations.

Raj Shankar

SVP Product, Calabrio

Our free to paid conversion rate doubled after implementing AssemblyAI.

Colin Treseler

Founder & CEO, Supernormal

The accuracy was strong, but the great documentation and unique models like Auto Chapters and Sentiment Analysis is what really won us over.

Nathan Webb

Product Manager, Aloware

Calls are and will remain a pertinent part of the customer service journey. Customer service isn't moving entirely to chatbots or chat interactions.

Dr. Shane Lynn

CEO, EdgeTier

Common questions

: It depends on how much of the stack you want to own. The Voice Agent API is a fully managed pipeline: one WebSocket handles STT, LLM, and TTS with about 1 second end-to-end latency. Realtime Speech-to-Text API gives you full architectural control when you already have an orchestrator, LLM, and TTS. A third option for sophisticated builds: if your orchestrator already handles VAD and turn detection, the Sync Speech-to-Text API transcribes each finished utterance in a single HTTP request with no streaming connection to manage.
: Both APIs support common voice-agent stacks including LiveKit, Pipecat, Python SDKs, Twilio SIP, and custom WebSocket clients. The Voice Agent API is the fastest path when you want AssemblyAI to own the full pipeline; Streaming STT fits teams that already own the rest of the stack.
: Voice Agent API delivers about 1 second end-to-end latency at a flat hourly rate covering speech recognition, LLM reasoning, and voice. Realtime Speech-to-Text API is priced for the STT layer only and is ideal when you want to bring your own orchestration and downstream providers.
: Yes. Both APIs share AssemblyAI speech model foundations, so teams often prototype with the Voice Agent API and move individual layers to Streaming STT as they need more control over routing, custom tooling, or provider choices.
: If you already use an orchestrator like LiveKit or Pipecat with your own LLM and TTS providers, Realtime Speech-to-Text API is the natural fit. If you are starting from scratch or want to replace multiple vendors with one managed connection, use the Voice Agent API.

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