Voice AI startup Rime has announced a $24 million Series A funding round as it seeks to help large organisations automate customer phone calls more effectively. The San Francisco-based company, founded in 2022 by former Stanford PhD student Lily Clifford, ex-Amazon Alexa engineer Brooke Larson, and Stanford engineer Ares Geovanos, says it now handles over 100 million calls each month for clients in food service, healthcare, airlines, and fintech.
Unlike many rivals that scrape the web for audio data, Rime has built its own recording studio in San Francisco to collect conversational data. This approach allows the startup to tune its voice models for accurate pronunciation of brand names and industry-specific terms, reducing the need for enterprises to retrain models for their sector. The company employs a phoneme-based architecture to adapt to different pronunciations automatically.
Despite progress in voice AI, Clifford acknowledged that many businesses still prefer legacy interactive voice response (IVR) systems. 'The voice technology is still not there to automate the vast majority of enterprise phone calls. LLMs have made it a lot easier to build voice applications that work, but they haven't changed how it feels to interact,' she said. Rime is now shifting from separate models for speech-to-text, text-to-speech, and language processing toward integrated speech-to-speech models to reduce latency and improve handling of background noise.
The funding round was led by M13 Ventures, with participation from Twilio Ventures, Corazon Capital, and Unusual Ventures. Morgan Blumberg of M13 will join Rime's board. The startup previously raised $5.5 million in a seed round in May 2025. Rime recently hired Rafael Valle, formerly of Meta's audio understanding team and Nvidia's deep learning audio research, as chief scientist.
For UK businesses, the development signals growing competition in voice AI for customer service. The UK's Information Commissioner's Office (ICO) requires transparency in automated call handling, and the EU AI Act imposes stricter rules on AI systems used in customer interactions. Rime's focus on low latency and reliability in regulated environments may appeal to British firms in financial services and healthcare, where compliance is critical. However, experts caution that voice AI still struggles with complex queries and emotional nuance, meaning full automation of customer calls remains some way off.