What is Ultravox?
Ultravox is a real-time voice AI platform for building fast, natural voice agents for phone and web, built on its speech-native model. It was created by the Seattle team formerly known as Fixie, founded in 2022 by Google and Apple veterans, and was acquired by Inworld AI in October 2026. Ultravox continues to operate, and its built-in voices now use Inworld's Realtime TTS-2.
Ultravox's difference is its model, which takes speech directly as input instead of converting it to text first, helping with low latency, turn-taking and interruptions. The Ultravox model has been released as open weights, which earned it a strong developer following. The hosted platform adds telephony through SIP, outbound call scheduling, custom voice clones and retrieval over your documents. Teams use it for customer support lines, appointment booking, sales calls and voice assistants inside apps.
Main Features
- Build voice agents on a speech-native model that listens to audio directly.
- Handle natural turn-taking and interruptions in real time.
- Connect phone calls through SIP and schedule outbound calls on Pro.
- Ground answers in your documents with RAG corpora.
- Create custom voice clones, from 1 on Pay As You Go to 5 on Pro.
- Test agents in an unlimited playground.
- Scale without surge pricing or hard concurrency caps on Pro.
How to Get Started with Ultravox
- Sign up at ultravox.ai to get 30 free minutes.
- Create an agent with a system prompt, voice and tools in the console.
- Test it in the playground, then connect a phone number via SIP or embed it in your app.
- Upgrade to Pro when you need unlimited concurrency and outbound scheduling.
Ultravox Pricing
Pay As You Go costs $0 per month and includes 30 free minutes, then $0.05 per minute, with up to 5 concurrent calls. Pro costs $100 per month at the same $0.05 per minute and removes concurrency caps, adds the outbound call scheduler, 5 custom voices and 20 RAG corpora. SIP costs about half a cent per minute, and Enterprise pricing is custom.
Who Should Use It?
- Developers building phone-based voice agents.
- Customer support teams automating calls.
- Startups building voice assistants into apps.
- Companies running outbound reminder or sales calls.
- Researchers interested in open-weight speech models.
Ultravox Alternatives
- Vapi: voice agent platform that mixes many model providers
- Retell AI: phone agents with a no-code builder
- Inworld TTS: the parent company's TTS for custom voice pipelines
Frequently Asked Questions
Is Ultravox free?
Partly. Ultravox gives 30 free minutes, then charges $0.05 per minute with no monthly fee on Pay As You Go.
What is Ultravox used for?
Ultravox is used to build real-time voice AI agents. Companies use it for phone support, booking and voice assistants.
Who owns Ultravox?
Inworld AI acquired Ultravox in October 2026. The platform continues to run and existing voice IDs keep working.
Is the Ultravox model open source?
Yes, the Ultravox speech model has been released with open weights, while the hosted platform is a paid service.