Add backfill changelog entry for Oct 2025 – Mar 2026

Covers platform features (Squads v2, Composer, Simulations, Monitoring,
HIPAA/ZDR compliance, Consolidated Logs, Vapi Voices), new model/provider
support (GPT-5, Claude 4.5-4.6, Gemini 3, Grok 4, Cartesia sonic-3,
Inworld TTS, etc.), and developer tools (Structured Outputs, MCP
improvements, Warm Transfer, hooks, encrypted tool args).

https://claude.ai/code/session_01PKuW5yr6fMdr6mSwX5Gchy

Author: claude

fern/changelog/2026-03-31.mdx

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+# What's New: October 2025 – March 2026
+
+Here's a summary of everything we shipped from October 2025 through March 2026.
+
+---
+
+## Platform
+
+1. **Squads v2**: Visual builder to simplify sophisticated multi-assistant orchestration with seamless handoffs between specialized agents.
+
+2. **Composer (Alpha)**: Intelligent assistant inside the dashboard that allows you to describe what you need through plain text prompts to help build, adjust, and debug voice agents.
+
+3. **Simulations (Alpha)**: Voice agent testing feature to build confidence through enabling systematic, AI-powered testing in specific scenarios with evaluation of outcomes.
+
+4. **Monitoring & Issues**: Automated call quality monitoring with trigger-based issue detection, alerting, and resolution suggestions.
+
+5. **HIPAA with Data Retention**: New compliance mode with private storage and in-dashboard toggle/purchase flow — available for additional cost.
+
+6. **Zero Data Retention**: Compliance mode that keeps context data during call as needed to execute tasks and retains no data afterwards.
+
+7. **Consolidated Logs**: Unified log viewing into a single page.
+
+8. **Vapi Voices**: 12 new ultra-realistic voices released, optimized for latency and cost with adjustable speed controls exposed. 8 legacy voices deprecated.
+
+---
+
+## New Models & Provider Support
+
+### Transcriber Models (Speech-to-Text)
+
+- **Deepgram Nova-3 Languages** — Added Hebrew, Urdu, Tagalog, and Arabic bilingual support
+- **Cartesia Transcriber** — ink-whisper
+- **Soniox** — stt-rt-v4
+
+### Intelligence Models (LLM)
+
+- **GPT-5 Family** — OpenAI's latest intelligence models, including GPT-5, 5-Mini, 5-Nano, 5.1, 5.2, 5.4, 5.4-Mini, 5.4-Nano
+- **Claude 4.5–4.6** — Anthropic's latest intelligence models Sonnet 4.5, Opus 4.5, Opus 4.6, Sonnet 4.6
+- **Gemini 3 Flash** — Google's latest intelligence models
+- **Grok 4 Fast** — Reasoning and non-reasoning variants
+- **GPT Realtime Mini**
+
+### Voice Models (Text-to-Speech)
+
+- **Cartesia** — sonic-3, sonic-3-2026-01-12, sonic-3-2025-10-27
+- **WellSaid** — Caruso (new), legacy
+- **Inworld** — inworld-tts-1 (REST, original), inworld-tts-1.5-max (WebSocket, $10/M chars), inworld-tts-1.5-mini (WebSocket, $5/M chars)
+- **ElevenLabs Scribe v2**
+
+---
+
+## Developer Tools & API
+
+1. **Structured Outputs Improvements**: Updates to our AI-powered analysis and data extraction tool, including transient structured outputs, audio-based extraction, and regex extraction.
+
+2. **SIP Request Tool + DTMF over SIP INFO**
+
+3. **Variable Passing Between Tool Calls**
+
+4. **Encrypted Tool Arguments**
+
+5. **Low Confidence Speech Hook**
+
+6. **Time Elapsed Hook**
+
+7. **`assistant.speechStarted` Event**
+
+8. **MCP Improvements** — Bearer auth, `$ref` dereferencing, child tool messages/discovery
+
+9. **Warm Transfer Improvements** — SIP support, caller ID, context engineering, variable filling