AssemblyAI Voice Agent API

The AssemblyAI Voice Agent API launched in April 2026 as a fully managed speech-to-speech pipeline that bundles Universal-3 Pro streaming transcription, an LLM gateway, and AssemblyAI-TTS-1 synthesis behind a single WebSocket connection. Priced at a flat $4.50 per hour, the billing model covers every component without concurrency fees, making cost forecasting straightforward for teams deploying at any scale. The Universal-3 Pro STT backbone delivers 5.19% WER on the internal English voice-agent benchmark and covers 99 languages, while JSON Schema-based tool calling enables backend integrations with CRMs, ticketing systems, and inventory APIs within live sessions. Speech-aware turn detection reduces false cutoffs compared to fixed silence timers, and a 30-second reconnect window preserves session state through brief network interruptions. BYO LLM and BYO TTS options let teams substitute their own models as the stack matures. A $50 free-credit onboarding grant and official plugins for the LiveKit and Pipecat orchestration frameworks reduce time-to-first-call to under an hour for most developers. The unlimited-concurrency model removes the per-seat bottleneck common in tiered plans, making AssemblyAI Voice Agent API a practical starting point for voice AI startups that expect rapid volume growth.