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Voice Agent API
Streaming STT
Developer
Tool calling
Guardrails

AssemblyAI

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AssemblyAI is a developer-first Voice AI platform for teams that need accurate streaming speech-to-text, speech understanding, guardrails, and a managed Voice Agent API. It is especially relevant for builders who want production-grade voice conversations with turn detection, interruption handling, transcripts, tool calls, and WebSocket-based integration.

Quick facts

Inbound calls

Yes

Outbound calls

Yes

Human handoff

No

Setup difficulty

Technical

Pricing model

Per Minute

Developer friendly

Yes

Main use cases

  • Customer Support
  • Appointment Scheduling
  • Lead Qualification
  • Healthcare Intake

Supported industries

  • SaaS
  • Healthcare
  • Contact Centers
  • AI Products

Integrations

WebSocket API
Custom API
Tool calling
Twilio
LLM Gateway
Guardrails

Voice and call capabilities

Inbound calls

Supported

Outbound calls

Supported

Human handoff

Verify with vendor

Data and permissions

Voice agents may talk to customers, access records, record calls, and trigger external actions.

Can read customer data
Can write or update external systems
Can send messages
Can trigger workflows
Requires API keys
Records calls
Human approval available
Review audio and transcript retention, API key handling, temporary browser tokens, tool-call permissions, guardrails, and data residency needs before production use.

Useful for

  • Developer teams
  • Real-time voice agents
  • Streaming speech accuracy

Not ideal for

  • Non-technical teams wanting no-code phone setup
  • Buyers needing a fully packaged receptionist
  • Teams that want telephony, CRM, and campaign tooling bundled together

Implementation notes

Strong fit when speech recognition quality and a developer-controlled voice stack matter. Test turn detection, interruption behavior, tool-call timing, telephony integration, and fallback paths with realistic call audio.

Pricing notes

AssemblyAI lists pay-as-you-go Voice Agent API pricing at $4.50/hr ($0.075/min), with separate streaming STT, speech understanding, guardrails, and LLM Gateway pricing depending on architecture. Verify current pricing before launch.

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