AssemblyAI Voice Agent API vs Vogent API

AssemblyAI Voice Agent API

One $0.075 a minute rate covers speech-to-text, the managed model, speech output, recordings and hosting, and the socket has an AsyncAPI file, typed error codes and a 30-second resume window. No concurrent-session limit is published, the status page has no Voice Agent component, and phone calls are inbound only through a Twilio trunk the customer owns.

Vogent API

IVR detection and navigation models for outbound calls. No public changelog and no release found since January 2026.

AssemblyAI Voice Agent API

1. Send session.end before closing the socket. Without it the session stays resumable, and billed, for 30 seconds
2. Retry only at_capacity, concurrency_exceeded and internal_error, with backoff. Every other session error code is fatal
3. Send tool.result inside the reply.done handler, not straight after tool.call
4. Mint a one-time token with GET /v1/token for browser clients and never ship the API key to a page
5. Deduplicate webhooks on event_id, and verify X-AAI-Signature against the raw body bytes because a 401 is not retried

Vogent API

1. Send an idempotencyKey on POST /dials, a reused key returns 409
2. Create a call with callAgentId, plus toNumber and fromNumberId for phone calls
3. Tell the model when to emit <|transfer|>, since transfers fire on that tag
4. Verify webhooks with the HMAC in X-Elto-Signature
5. Expect new dials to fail at the workspace's concurrent dial limit until calls end