Build a voice agent in JavaScript with Vercel AI SDK

How do voice agents work? At its core, a voice agent operates by completing three fundamental steps: Listen - Capture audio and transcribe it into text. Think - Interpret the intent and decide how to respond.. Speak - Convert the response into audio and deliver it. In real-world applications, voice agents typically use one of two primary design frameworks: 1. STT > Agent > TTS Architecture In the Sandwich architecture, speech-to-text (STT) converts the user's spoken audio into accurate text using AI models like Whisper/Gladia, a text-based Vercel AI agent then processes that text with an LLM to understand intent, reason, and generate a smart reply (often with tools), and text-to-speech (TTS) finally transforms the agent's text response back into natural-sounding spoken audio (via models like OpenAI TTS or ElevenLabs) for playback to the user. Pros - Full control over each component (STT/TTS providers as needed). Full streaming support creates responsive, real-time voice feel. Deploys s