Voice AI startup Rime has raised $24 million in Series A funding led by M13 Ventures, with participation from Twilio Ventures, Corazon Capital, and Unusual Ventures.

The San Francisco-based company builds voice AI models trained on conversational data it records in its own studio, rather than scraping audio from the web.

Founded in 2022 by former Stanford PhD student Lily Clifford, ex-Amazon Alexa engineer Brooke Larson, and Stanford engineer Ares Geovanos, Rime uses a phoneme-based architecture to handle pronunciation of brand-specific and industry terms without requiring customers to retrain models.

The startup initially operated a pipeline of separate models for speech-to-text, text-to-speech, and a large language model, but is now shifting toward developing speech-to-speech models that reduce latency, improve turn-taking, and handle background noise, while reducing reliance on orchestration across multiple models.

Clifford noted that enterprises still prefer legacy IVR systems because current AI voice technology cannot yet automate the majority of enterprise phone calls; LLMs have made building voice applications easier but have not meaningfully changed the user experience, which she described as akin to a new IVR with a better voice.

Rime claims customers stay longer on calls due to its training data and model positioning, helping it win enterprise contracts with clients such as Mayo Clinic, Dialpad, Upstart, and Asurion.

The company serves food service, healthcare, airline, and fintech customers. With the new funding, Rime plans to expand its team of 35, hiring for model development, engineering, and partnerships.

The company recently appointed Rafael Valle, formerly of Meta Superintelligence Labs and NVIDIA’s applied deep learning audio research team, as Chief Scientist.

M13’s Morgan Blumberg, who is joining the board, said that while companies like ElevenLabs have moved into orchestration and application layers, Rime‘s focus on advancing the core model with low latency and high reliability in regulated environments differentiates it.

Rime had previously raised $5.5 million in a seed round in May 2023.