Add changelog (#362)

Author: quantstruct-bot

fern/changelog/2025-04-23.mdx

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+1. **Create Sesame Voices Programmatically**: You can now create and manage [Sesame Voices](https://api.vapi.ai/api#:~:text=CreateSesameVoiceDTO) via the API by specifying a `voiceName` and `transcription`.
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+2. **AWS STS Support in OAuth2 Authentication**: You can now use AWS Security Token Service for authentication by setting the `type` of `OAuth2AuthenticationPlan` to `'aws-sts'`, enabling integration with AWS's secure token services.

fern/changelog/2025-04-24.mdx

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+1. **Per-Voice Caching Control Added**: Developers can now enable or disable voice caching for each assistant's voice using the new `cachingEnabled` property in voice configurations. This allows you to optimize performance or comply with data policies by controlling whether voice responses are cached.
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+2. **'Condition' Value Now Accepts Strings**: When specifying conditions, the `value` property should now be provided as a string instead of an object. This simplifies condition definitions and makes it easier to set and interpret condition values.

fern/changelog/2025-04-25.mdx

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+1. **New OpenAI Models 'o3' and 'o4-mini' Added**: You can now use the '`o3`' and '`o4-mini`' models with OpenAI models in `Assistant.model["OpenAIModel"].model`.
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+2. **'whisper' Model Added to Deepgram Transcribers**: The '`whisper`' model is now available in [Deepgram transcriber](https://api.vapi.ai/api#:~:text=DeepgramTranscriber) models for audio transcription. Select '`whisper`' in the `Assistant.transcriber["DeepgramTranscriber"].model` property to utilize this advanced transcription model.
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+3. **Expanded Language Support in Deepgram Transcribers**: You can now transcribe audio in '`ar`' (Arabic), '`he`' (Hebrew), and '`ur`' (Urdu) when using Deepgram transcriber in your assistant.

fern/changelog/2025-04-26.mdx

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+1. **Adding metadata to ToolCallResult and ToolCallResultMessage**: You can now include optional metadata in tool call results and messages. This allows you to send additional context or information to clients alongside standard tool responses.
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+2. **Adding `tool.completed` client message type**: Assistants can now handle a new client message type, `tool.completed`. This enables you to notify clients when a tool has finished executing.
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+3. **Customizable assistant messages via `message` property in [ToolCallResult](https://api.vapi.ai/api#:~:text=ToolCallResult)**: You can now specify exact messages for the assistant to say upon tool completion or failure using the `message` property. This gives you greater control over user interactions by allowing custom, context-specific responses.

fern/changelog/2025-04-27.mdx

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+1. **New Assistant Hook for Call Ending Events**: You can now define actions to execute when a call is ending using [`Assistant.hooks\["AssistantHookCallEnding"\]`](https://api.vapi.ai/api#:~:text=AssistantHookCallEnding). This allows you to specify actions like transferring the call, saying a message, or invoking a function at the end of a call.
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+2. **Enhanced Voicemail Detection Configuration**: Configure voicemail detection more precisely with new `Assistant.voicemailDetection.backoffPlan` and `Assistant.voicemailDetection.beepMaxAwaitSeconds` properties. This lets you control retry strategies and set maximum wait times for voicemail beeps.
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+3. **Twilio Authentication Using API Keys**: Authenticate with Twilio using `apiKey` and `apiSecret` when importing a [Twilio Phone Number](https://dashboard.vapi.ai/phone-numbers/) This replaces the need for `authToken`. 
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+4. **Support for New Voicemail Detection Provider and Model**: Utilize the new `vapi` provider for voicemail detection by configuring `Assistant.voicemailDetection.provider`. Additionally, the `gemini-2.5-flash-preview-04-17` model is now supported in various schemas for advanced capabilities.
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+5. **Expanded Workflow Nodes**: Workflows now support `Start` and `Assistant` nodes, enabling more complex and customizable call flow designs. This allows for greater flexibility in defining how calls are handled.