Ultravox
Category: Voice / Speech AI
Seattle voice AI lab and platform (formerly Fixie.ai) that trains open-weight speech-native models and offers a real-time voice agent API. Acquired by Inworld in 2026. Ultravox was founded in 2022. The company is led by Zach Koch. Based in Seattle, United States. Team size: 11-50. Total funding raised: $17M. Latest round: Acquired. Key investors include Redpoint Ventures, Madrona Venture Group, SignalFire, Bloomberg Beta, Kearny Jackson, Plug and Play.
- Founded
- 2022
- Headquarters
- Seattle, United States
- Team size
- 11-50
- Total funding
- $17M
Value proposition
A speech-native model processes audio directly instead of transcribing it to text first. Combined with Ultravox's fully owned inference stack and infrastructure, this cuts latency and keeps paralinguistic cues such as tone, cadence and pitch, so voice agents sound fast and natural.
Products and solutions
Ultravox Realtime Platform (REST APIs, SDKs for web and mobile, built-in tools, telephony integrations), Ultravox v0.7 open-weight speech-native model, UltraVAD v0.1 neural voice activity detection and turn-taking model, earlier Fixie LLM agent platform
Unique value
Speech-native, open-weight model running on dedicated in-house inference. The company claims state-of-the-art Big Bench Audio scores (91.8% without reasoning, 97% with thinking) at real-time latency, priced at 5 cents per minute including TTS.
Target customer
Developers and companies building real-time voice agents, from startups to enterprises, including telephony-based agents.
Industries served
Customer service and contact centers, sales automation, conversational AI apps, telephony
Technology advantage
End-to-end ownership of the speech model, inference stack and infrastructure. Specific strengths are turn-taking and interruption handling (UltraVAD) and open-weight models published on Hugging Face.
How they differentiate
Competitors like Vapi and Retell chain STT, LLM and TTS in a pipeline. Ultravox uses a single speech-native model on its own infrastructure. Unlike OpenAI Realtime and Gemini Live, its models are open-weight.
Main competitors
Vapi, Retell AI, OpenAI gpt-realtime / Realtime API
Key partnerships
Inworld AI (TTS partnership for more than a year before the acquisition), integrations with major telephony providers, open-weight models published on Hugging Face
Notable customers
11x
Major milestones
2022: founded as Fixie.ai in Seattle. 2023-03: $17M seed led by Redpoint. Later pivoted and rebranded to Ultravox (speech-native voice AI). Released Ultravox v0.7 and UltraVAD v0.1 open-weight models. 2026-09/10: acquired by Inworld for an undisclosed sum, with Ultravox customers' built-in Inworld voices upgraded to Realtime TTS-2.
Growth metrics
The company says 'thousands of teams' build on the platform.
Market positioning
Developer-focused real-time voice agent infrastructure and research lab. After the acquisition it is positioned as Inworld's speech-to-speech and voice-agent platform.
Geographic focus
Global, US-based
About Zach Koch
Co-founder and CPO of Fixie.ai (2022), later CEO of the company after it rebranded to Ultravox. Part of the founding team GeekWire described as 'Google and Apple vets'. After the 2026 Inworld acquisition, his LinkedIn reportedly lists him as VP of Product at Shopify (GeekWire, 2026).
Latest news about Ultravox
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Official website: https://www.ultravox.ai