Added directions for Cartesia custom voices.

fern/customization/custom-voices/cartesia.mdx

@@ -0,0 +1,27 @@
+---
+title: Cartesia
+subtitle: Set up a custom Cartesia voice in Vapi
+description: Use a custom Cartesia voice in Vapi by connecting your Cartesia API key and selecting your voice.
+slug: customization/custom-voices/cartesia
+---
+
+This guide shows you how to use a voice you created with Cartesia in your Vapi assistant. Cartesia's prebuilt voices are already available in the [Voice Library](/providers/voice/overview); follow this page only to use your own custom voice.
+
+<Note>A Cartesia account and API key are required for this process.</Note>
+
+<Steps>
+  <Step title="Create a Cartesia account and voice">
+    Sign up at [Cartesia](https://play.cartesia.ai), then create a custom voice in the [Cartesia playground](https://play.cartesia.ai/voices). 
+  </Step>
+  <Step title="Retrieve your Cartesia API key">
+    Get your API key from your Cartesia account.
+  </Step>
+  <Step title="Enter your API key in Vapi">
+    In the [Vapi Dashboard](https://dashboard.vapi.ai), open **Settings**, then **Integrations**, and add your Cartesia API key under **Cartesia**.
+
+    Once you save, your Cartesia voices sync automatically.
+  </Step>
+  <Step title="Select your custom voice">
+    Open an assistant and open **Voice Settings**. Choose **Cartesia** as the provider and select your voice, or switch to **Custom Voice ID** and paste your Cartesia voice ID. You can find your voice ID in the [Voice Library](/providers/voice/overview).
+  </Step>
+</Steps>

fern/docs.yml

@@ -246,6 +246,8 @@ navigation:
                 path: customization/custom-voices/elevenlabs.mdx
               - page: PlayHT
                 path: customization/custom-voices/playht.mdx
+              - page: Cartesia
+                path: customization/custom-voices/cartesia.mdx
           - page: Custom transcriber
             path: customization/custom-transcriber.mdx
             icon: fa-light fa-microphone
@@ -599,6 +601,7 @@ navigation:
             icon: fa-light fa-link
             contents:
               - section: Voices (Text-to-speech)
+                path: providers/voice/overview.mdx
                 icon: fa-light fa-waveform-lines
                 contents:
                   - section: Vapi Voices

fern/providers/voice/overview.mdx

@@ -0,0 +1,67 @@
+---
+title: Voices (Text-to-speech)
+subtitle: Find, preview, and use voices from any supported provider
+description: Find, preview, and use text-to-speech voices from any Vapi-supported provider, and look up a voiceId in the Vapi dashboard.
+slug: providers/voice/overview
+---
+
+Vapi supports text-to-speech (TTS) voices from many providers. You choose a voice
+by setting the `provider` and `voiceId` on your assistant's `voice` configuration.
+See [Create Assistant](/api-reference/assistants/create) in the API reference.
+
+```bash title="Set an assistant's voice"
+curl -X PATCH "https://api.vapi.ai/assistant/ASSISTANT_ID" \
+  -H "Authorization: Bearer $VAPI_API_KEY" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "voice": {
+      "provider": "PROVIDER",
+      "voiceId": "VOICE_ID"
+    }
+  }'
+```
+
+This page shows you how to find a `voiceId` in the dashboard, and links to every
+supported provider.
+
+## Find a voice in the dashboard
+
+The **Voice Library** in the [Vapi Dashboard](https://dashboard.vapi.ai) lists every
+voice available to your organization. Browse and preview voices there, then copy a
+voice's ID to use on an assistant.
+
+<Steps>
+  <Step title="Browse and preview">
+    In the [Vapi Dashboard](https://dashboard.vapi.ai), open **Resources**, then
+    **Voice Library**. Filter by **Provider** and search by name. Press play on a
+    voice to preview it.
+  </Step>
+  <Step title="Copy the voice ID">
+    Click the copy icon on a voice to copy its ID.
+  </Step>
+  <Step title="Use it on an assistant">
+    Open an assistant and click the edit (pencil) icon on the **Voice** card to
+    open **Voice Settings**. Choose the **Provider** and **Voice**, or paste the
+    copied ID under **Custom Voice ID**.
+  </Step>
+</Steps>
+
+<Tip>
+  Some providers also let you use your own custom voice. See [Custom voices](/customization/custom-voices/custom-voice) for setup.
+</Tip>
+
+## Supported voice providers
+
+<CardGroup cols={2}>
+  <Card title="Vapi Voices" href="/providers/voice/vapi-voices" />
+  <Card title="ElevenLabs" href="/providers/voice/elevenlabs" />
+  <Card title="PlayHT" href="/providers/voice/playht" />
+  <Card title="Azure" href="/providers/voice/azure" />
+  <Card title="OpenAI" href="/providers/voice/openai" />
+  <Card title="Cartesia" href="/providers/voice/cartesia" />
+  <Card title="LMNT" href="/providers/voice/imnt" />
+  <Card title="Minimax" href="/providers/voice/minimax" />
+  <Card title="RimeAI" href="/providers/voice/rimeai" />
+  <Card title="Deepgram" href="/providers/voice/deepgram" />
+  <Card title="Inworld" href="/providers/voice/inworld" />
+</CardGroup>