Fixie.ai

Fixie.ai builds speech-understanding models and a platform for developers and enterprises creating real-time voice agents. It became Ultravox AI in 2025, formalizing its focus on voice technology. Its products include the Ultravox model and Ultravox Realtime, a managed platform for building and scaling voice agents. Developers can build mobile voice experiences, integrate the service into Pipecat applications, and transfer calls to human operators with conversation context.

Founded in 2022, the company is led by cofounder and CEO Zach Koch. Ultravox cofounder Zhongqiang Huang served as chief research officer in 2025. The team's technical approach connects an audio encoder to an existing language model through a trained multimodal projector, mapping audio into the model's internal representation without a separate transcription stage. The core model accepts audio and produces streaming text; the Realtime service supplies the complete spoken interaction.

Developers can download model weights and use the published training code, or access managed APIs. The commercial platform offers free entry-level access and paid plans extending to enterprise service levels. In December 2025, Ultravox reported that its customer base was 18 times its size at the end of 2024, although it did not disclose an absolute customer count.