One API to build voice agents
Stream audio in, get audio back. We handle the rest so you can focus on your product.
The most accurate voice agent,
where it matters most
Universal-3 Pro Streaming gets the hard stuff right — emails, phone numbers, order IDs, names. The things that let your voice agent complete the tasks your customers need.
00:00 / 01:34
Agent Thanks for calling the prescription refill line. This is Priya. Can I have your date of birth and the RX number on the bottle?
caller Date of birth is 10/10/51, and the prescription is RX-7704132. It’s Metropolol 80mg.
Agent Got it. I’m also seeing a standing order from Dr. Chen for epinephrine, 0.25 milligrams, 1:1,000 IM. Do you want that refilled too?
Agent Yes, please. And can you send it to the address on file, 10631 Northeast Knott Street, Portland, Oregon 97220?
Agent Confirmed. I’ll route it to your MyChart, and you’ll get a text at (971) 235-7292 when it’s all ready, around 08:30 tomorrow.
Agent Thanks for calling the prescription refill line. This is Priya. Can I have your date of birth and the RX number on the bottle?
caller Date of birth is 10/1051, and the prescription is dash seven seven zero four one three two. It’s metoprolol eighty milligrams.
Agent Got it. I’m also seeing a standing order from Dr. Chen for epinephrine point two five milligrams one to thousand I’m. Do you want that refilled too?
Caller Yes, please. And can you send it to the address on file, 10631 Northeast Knott Street, Portland, Oregon 97220?
Agent Confirmed. I’ll route it to your MyChart, and you’ll get a text at (971) 235-7292 when it’s all ready, around o 08:30 tomorrow.
Conversations that flow naturally
A proprietary Voice AI stack built end-to-end for speech, so every layer is tuned for how people actually talk.
The most accurate voice agents on the market
Powered by our proprietary Voice AI models like Universal-3-Pro Streaming- Clean interruption handling + turn detection
Speech-aware VAD knows the difference between "I'm thinking" and "I'm done." Your agent stops cutting people off. - ~1 second response time
Fast enough that the rhythm of conversation holds. - Built for what's coming
Because we own the stack, improvements across speech understanding, reasoning, and voice generation ship as one product.
The fastest way from idea to working voice agent
One WebSocket. A handful of JSON types. Most developers ship the same day.
- Standard JSON API
No SDKs, no frameworks, no new billing dashboard. The same primitives you already know. - Live configuration updates
Update system prompt, voice, tools, and VAD settings mid-conversation. Change anything and see it instantly. - Tool calling integrations
Register any function with JSON Schema. The agent calls it when appropriate — look up an account, check an order, trigger a workflow. - Session resumption
Reconnect within 30 seconds if the WebSocket drops. Context preserved, conversation continues.
See how AssemblyAI stacks up against the other voice agent API options.
AssemblyAI API Voice Agent API $4.50/hr | OpenAI Realtime API ~$18/hr | Deepgram Voice Agent API ~$4.50/hr | |
|---|---|---|---|
ASR model | Universal-3 Pro Streaming #1 Wer | Gpt-realtime | Deepgram Nova-3 |
Alphanumeric accuracy | 16.7% | 23.3% | 25.5% |
Billing model | Flat hourly, no commitments | Per-token audio | Flat hourly; commitments required |
Language Support | EN, ES, FR, DE, IT, PT | 99+ languages (low accuracy) | EN, ES, NL, FR, DE, IT, JA |
End-to-end latency | ~1 second | ~1 second | ~1–1.5 seconds |
Turn detection | Speech-aware VAD | Basic | Basic |
Turn detection tuning | Semantic + Neural Network + VAD | Semantic VAD and traditional VAD | Traditional VAD only |
Mid-session updates | Prompt + voice + tools + turn detection | Prompt + tools only | Prompt + voice only |
Session resumption | 30s reconnect window | — | — |
Barge in | Intelligent interruption | VAD based interruptions | VAD based interruptions |
Tool calling behavior | Handles with intermediate speech | Goes silent | Goes silent |
Pricing estimates based on publicly available data as of 2026. Actual costs vary by usage pattern.
Don't take our word for it. Talk to it.
The best way to evaluate a voice agent platform is to have a conversation with one. Try the live demo — no signup required.
Invisible infrastructure for your voice product
Your customers should feel like you built it. Full control over conversation design, tool integrations, and agent behavior.
Customer Support
AI Companions
Clinical Workflows
Language Learning
Phone Agents
Coaching & Training
More on Voice Agents
Voice Agent Solutions
Create voice experiences that feel more intuitive and responsive while maintaining the flexibility to optimize for your unique requirements.
Using an orchestrator?
Universal-3 Pro Streaming gives your voice agents the accuracy, speed, and real-time control to handle real conversations at scale.
Frequently Asked Questions
AssemblyAI's Voice Agent API is a single WebSocket API that handles the full voice agent pipeline — speech understanding, LLM reasoning, voice generation, turn detection, and interruption handling — so developers can stream audio in and get audio back without stitching together separate services. It's powered by Universal-3 Pro for industry-leading speech recognition accuracy and supports tool calling, live mid-conversation configuration updates, and 10-second session resumption. The API currently supports English, Spanish, French, German, Italian, and Portuguese.
The Voice Agent API costs a flat $4.50 per hour, covering the entire speech-to-speech pipeline with no per-token surcharges or concurrency caps. The OpenAI Realtime API costs roughly $18 per hour and bills per token across 30+ event types, while Deepgram's voice agent offering is also $4.50 per hour but uses concurrency-metered billing. AssemblyAI's flat-rate model means predictable costs at any scale — from a single call to thousands of concurrent sessions.
Transcription errors cascade through every downstream step — if your agent mishears an order number, email address, or customer name, it can't complete the task. Universal-3 Pro gets the hard stuff right: mixed-entity tokens like confirmation codes, phone numbers, and proper nouns that voice agents need to act on. In head-to-head comparisons, it delivers 92.7% mixed-entity accuracy and handles natural pauses through semantic turn detection rather than basic silence-based VAD.
Common use cases include customer support agents that look up orders and resolve issues by voice, AI companions, clinical workflow assistants (with Medical Mode for healthcare terminology accuracy), phone-based agents for appointment scheduling and lead qualification, language learning tools with real-time feedback, and coaching and training applications. The API's native tool calling lets your agent execute functions — lookups, payments, workflows — mid-conversation without breaking the dialogue flow.
Sign up for a free account, grab an API key, and connect via WebSocket using standard JSON messages — no proprietary SDK required. Most developers ship a working demo same day. For a hands-on walkthrough, explore the developer docs. You can also talk to the live demo on the product page to experience the API's accuracy and latency firsthand.
The Voice Agent API is the fastest path to production—one integration, sub-second latency, no stitching required. But if you're already invested in an orchestrator like LiveKit or Pipecat, you can use Universal-Streaming as the STT layer in that stack. Both work. The API just gets you there faster.
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