Cartesia AI

Cartesia builds the Sonic text-to-speech model, designed specifically for real-time voice AI applications. Sonic delivers sub-100ms latency—faster than the blink of an eye—making it the fastest production TTS available for conversational AI.

What sets Cartesia apart is naturalness. Sonic generates speech that laughs, expresses emotion, and handles real-world text intelligently, including proper pronunciation of acronyms, initialisms, and alphanumerics based on context. The model supports 40+ languages covering 95% of global markets, with particularly strong performance in Hindi and eight other Indian languages.

Developers can access Sonic through a straightforward API and SDKs, with a playground for rapid prototyping. Voice customization options include a curated library of conversational voices and both instant 10-second cloning and professional voice cloning for enterprise needs. Cartesia is SOC 2 Type II certified, HIPAA compliant, and PCI Level 1 certified, meeting enterprise security requirements.

Vapi and Cartesia integrate to deliver voice agents with human-level conversational speed. Cartesia's Sonic model provides the text-to-speech layer within Vapi's voice AI platform, converting LLM responses to natural speech in under 100ms.

This latency advantage directly impacts user experience. Voice agents built with Vapi and Cartesia respond within the 200ms threshold humans expect in natural conversation, eliminating the awkward pauses that make AI interactions feel robotic. Sonic's emotional expressiveness—including laughter and dynamic intonation—adds another layer of naturalness that keeps users engaged.

The integration supports global deployment through Sonic's multilingual capabilities, enabling Vapi developers to build voice agents that speak natively in dozens of languages without sacrificing quality or speed. For enterprises in healthcare, finance, hospitality, and customer service, the combination provides a complete voice AI stack that meets both performance requirements and compliance standards. Vapi handles orchestration, conversation management, and telephony; Cartesia delivers the voice that makes agents sound genuinely human.