KugelAudio has a built-in Vapi custom TTS endpoint — no proxy server needed. Just point your Vapi assistant at our API and you’re done.
Setup
1. Get your KugelAudio API key and a voice ID
Pick whichever flow you prefer — the dashboard is faster for one-offs, the API is better for scripted setup.
Open the assistant
In the Vapi dashboard, open the assistant you want to use.
Go to Voice → Provider
Click Voice, then Provider.
Pick Custom Provider
Scroll down in the provider list and select Custom Provider.
Save
Save the assistant. The voice is now powered by KugelAudio.
The “Voice ID” field inside Vapi’s UI has no effect when using a custom provider — the voice_id query param in the URL is what selects the voice.
Use PATCH /assistant/{id} to update an existing assistant, or include the voice field when creating a new one with POST /assistant:
voice_id — the numeric voice ID from Step 1.api_key — your KugelAudio API key. KugelAudio authenticates it on every request.
As an alternative, you can pass the API key in Vapi’s server.secret field instead of the URL. Vapi will send it as the x-vapi-secret header on every request and KugelAudio will authenticate it the same way.
To select a specific model, add &model_id=kugel-3 (recommended) or &model_id=kugel-3 (lowest latency) to the URL.
How it works
Vapi sends one POST per phrase to /vapi/synthesize:
KugelAudio streams back raw PCM16 at the requested sample rate — exactly what Vapi expects.
