Vapi supports using a custom transcription service via a WebSocket integration, allowing you to use your own transcriber while leveraging Vapi’s text-to-speech SDK although direct custom TTS integration isn’t officially supported, you can deploy your own TTS server as a workaround, and Vapi’s scalable, enterprise-grade infrastructure can support large-scale company deployments..
https://docs.vapi.ai/customization/custom-transcriber