chore(changelog): add 2025-06-20.mdx with API changes summary

Author: quantstruct-bot

fern/changelog/2025-06-20.mdx

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+---
+title: Changelog – 2025-06-20
+---
+
+# Changelog – 2025-06-20
+
+## API Changes Overview
+
+This release brings significant enhancements for Vapi developers, with a focus on new campaign management, improved tool integration, and expanded credential support. Below is a summary of the most impactful changes since the last published changelog (2025-06-18):
+
+### 🚀 New Features
+- **Campaign Management API**
+  - New endpoints and schemas for Campaign, CreateCampaignDTO, and UpdateCampaignDTO.
+  - Enables scheduling, tracking, and managing outbound campaigns, including customer lists, schedule plans, and call assignment.
+  - Campaigns now support status tracking (`scheduled`, `in-progress`, `ended`) and rich metadata (e.g., ended reason, calls counter).
+- **API Request Tool**
+  - New `ApiRequestTool` schema and endpoints for defining and executing API requests within Vapi workflows.
+  - Customizable headers, bodies, and variable extraction plans are now supported.
+  - Enhanced error handling and retry logic via `backoffPlan`.
+- **Credential Management**
+  - Added support for new credential types: S3, GCP, Azure, Supabase, Cloudflare, and more.
+  - Credentials can be associated at the workflow and assistant levels, allowing dynamic credential injection and fallback ordering (`fallbackIndex`).
+- **Transcriber and Voice Enhancements**
+  - Support for new transcriber providers and fallback plans, including AssemblyAI, Azure, Deepgram, and others.
+  - Workflow and assistant schemas now include advanced voice and transcriber configuration, with fallback and denoising options.
+
+### 🛠️ Improvements
+- **Workflow & Assistant Schema Expansion**
+  - Major expansion of `Workflow` and `Assistant` schemas to support:
+    - Voice and transcriber selection
+    - Credential and compliance plans
+    - Real-time monitoring and observability (Langfuse integration)
+    - Advanced speech denoising and artifact generation
+- **Client/Server Message Handling**
+  - Expanded support for new message types and improved configuration of client/server message flows.
+  - Enhanced template variable support for assistant messages using LiquidJS syntax.
+- **Error Handling**
+  - Added and expanded `endedReason` enums for calls and campaigns, providing more granular error and status reporting.
+
+### 🧹 Removals
+- Deprecated and removed `model` property from `Workflow` schema.
+- Removed unused/legacy schema paths: `LogicEdgeCondition`, `FailedEdgeCondition`, `Workflow` (legacy versions).
+
+### 📝 Migration Notes
+- **Campaigns:** If you are using campaigns, review the new API endpoints and schemas. Campaigns now must be created and updated using the new DTOs and support richer scheduling and reporting.
+- **Credentials:** When using new credential types or fallback logic, ensure your workflow and assistant definitions are updated to reference the new credential schemas and properties.
+- **Tool Integrations:** If you build or use custom tools, review the new `ApiRequestTool` and related DTOs for expanded functionality and error handling.
+
+---
+
+For full details and schema references, see the [OpenAPI documentation](../openapi) and the updated developer guides.
+
+*Published: 2025-06-20*