Add changelog for 2025-06-13 (#511)

Author: quantstruct-bot

fern/changelog/2025-06-13.mdx

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+# Background Speech Denoising, Cartesia Transcriber, Workflow Enhancements, and Call Error Handling
+
+1. **Background Speech Denoising Plan**: You can now enhance call quality by configuring advanced background speech denoising options using the new [`assistant.backgroundSpeechDenoisingPlan.smartDenoisingPlan`](https://api.vapi.ai/api#:~:text=SessionPaginatedResponse-,Assistant,-AssistantPaginatedResponse) (default: `false`), which replaces the previous `backgroundDenoisingEnabled` setting.
+
+<CardGroup cols={2}>
+  <Card title="Enable Smart Denoising (Krisp)" icon="volume-up">
+    Use the `SmartDenoisingPlan` to filter out background speech and noise using [Krisp technology](https://krisp.ai/).
+  </Card>
+  <Card title="Customize Fourier Denoising" icon="sliders">
+    Fine-tune noise reduction with the new `FourierDenoisingPlan` for more control over audio clarity.
+  </Card>
+</CardGroup>
+
+<Info>
+  Smart and Fourier denoising can be combined for optimal results. Order of precedence: Smart denoising, then Fourier denoising.
+</Info>
+
+2. **Workflow Server Property**: Workflows now support a [`server`](https://api.vapi.ai/api#:~:text=TrieveKnowledgeBaseImport-,Workflow,-UpdateWorkflowDTO) property, allowing you to specify a server URL to receive webhook callbacks for workflow events directly.
+
+3. **New Workflow Models**: You can now integrate Google's LLMs or custom models into your workflows by specifying [`Google`](https://api.vapi.ai/api#:~:text=WorkflowGoogleModel) or [`Custom LLM`](https://api.vapi.ai/api#:~:text=WorkflowCustomModel) in your workflow model settings. Select your model under [Model Settings](https://dashboard.vapi.ai/workflows#:~:text=Model%20Settings)
+
+<Frame caption="Workflow Google Custom LLM">
+  <img src="../static/images/changelog/workflow-google-custom-llm.png" alt="Workflow Google Custom LLM" />
+</Frame>
+
+4. **Enhanced Error Reporting for Cartesia Services**: A new `endedReason` value `pipeline-error-cartesia-502-server-error` has been added to help you identify and handle specific errors related to Cartesia server issues.
+
+5. **Enhanced Error Handling and Status Enums**: We've added new error enums and status codes to help you better handle and debug call-related issues:
+
+   - **VAPI Fault Errors**: Detect specific VAPI-related errors during call start using `call.start.error-vapifault-get-org` and `call.start.error-vapifault-get-subscription`
+   
+   - **Subscription Status Errors**: Identify subscription-related issues with new enums:
+     - `call.start.error-subscription-frozen` (replaces `unknown-error`)
+     - `call.start.error-subscription-insufficient-credits`
+   
+   - **Call Completion Statuses**: Track how calls are completed with new enums:
+     - `call.in-progress.twilio-completed-call`
+     - `call.in-progress.sip-completed-call`
+   
+   - **In-Call Error Detection**: Handle specific errors during active calls using enums like `call.in-progress.error-vapifault-chat-pipeline-failed-to-start`