---
name: edge-voice-agent-holds-call
title: "Edge Voice Agent That Holds a Call"
description: "Voice agent on Telnyx Edge Compute + Agent SDK — answers an inbound call and runs an STT → LLM → TTS conversation loop, all in the same PoP. Zero-credential inference via the [telnyx] binding."
language: nodejs
framework: telnyx-edge (Agent SDK)
telnyx_products: [Edge Compute, Voice, AI Inference]
---
# Edge Voice Agent That Holds a Call
Voice agent on Telnyx Edge Compute + Agent SDK — answers an inbound phone call and holds a conversation loop with streaming speech-to-text, LLM inference, and text-to-speech, all in the same PoP. Uses the `[telnyx]` binding for zero-credential inference — no API key in code for the LLM.
## Why Telnyx
Telnyx is an **AI Communications Infrastructure** platform — voice, messaging, SIP, AI, and IoT on one private, global network. This example composes Call Control, streaming transcription, text-to-speech, AI inference, and stateful actors on Edge Compute in a single deployable function — the flagship "voice agent that holds a call" that only Telnyx can ship because we own the telephony network.
## Telnyx API Endpoints Used
- **Call Control**: `POST /v2/calls/{call_control_id}/actions/answer` — answer the inbound call
- **Call Control TTS**: `POST /v2/calls/{call_control_id}/actions/speak` — text-to-speech for greeting and replies
- **Call Control Transcription**: `POST /v2/calls/{call_control_id}/actions/transcription_start` — streaming STT (Google engine, inbound track)
- **Call Control Transcription**: `POST /v2/calls/{call_control_id}/actions/transcription_stop` — stop STT before LLM turn
- **Call Control Hangup**: `POST /v2/calls/{call_control_id}/actions/hangup` — end the call
- **AI Inference**: `POST /v2/ai/openai/chat/completions` — via `this.env.TELNYX.ai.openai.chat.createCompletion()` (pre-authenticated binding, zero-credential)
## Architecture
```
Inbound call → webhook → VoiceAgent actor (one per call)
│
▼
┌────────────────────────────────────────────────────┐
│ call.initiated → answer() │
│ call.answered → speak(greeting) │
│ speak.ended → transcription_start() │
│ call.transcription (final) │
│ → appendUser(transcript) │
│ → stopTranscription() │
│ → respond() ────────────────────────────┐ │
│ │ │ │
│ ▼ Agent SDK (Stateful Actor) │ │
│ ┌────────────────────────────────┐ │ │
│ │ this.messages.toOpenAI() │ │ │
│ │ env.TELNYX.ai.openai.chat │ │ │
│ │ .createCompletion() │ │ │
│ │ this.messages.add("assistant") │ │ │
│ └────────────────────────────────┘ │ │
│ → speak(reply) ◄────────────────────────┘ │
│ speak.ended → transcription_start() (loop) │
│ call.hangup → finishCall() (state persisted) │
└────────────────────────────────────────────────────┘
```
## Environment Variables
| Variable | Type | Required | Description |
|----------|------|----------|-------------|
| `TELNYX_API_KEY` | secret | **yes** | Telnyx API key for Call Control REST (answer, speak, transcription, hangup) |
| `[telnyx]` binding | toml | **yes** | Pre-authenticated Telnyx client for zero-credential AI inference |
| `AI_MODEL` | env_var | no | Inference model name (default: `zai-org/GLM-5.2`) |
> **Agent / CLI access**
>
> ```bash
> # Buy a phone number for the voice agent
> telnyx number-orders create --phone-number "+16282564655"
>
> # List your numbers
> telnyx numbers list
> ```
## Setup
### Prerequisites
- [Telnyx Edge CLI](https://github.com/team-telnyx/edge-compute/releases) v0.2.2+
- Node.js 18+
- A Telnyx phone number with a Call Control application
### 1. Clone and install
```bash
git clone https://github.com/team-telnyx/telnyx-code-examples.git
cd telnyx-code-examples/edge-voice-agent-holds-call
npm install
```
### 2. Configure secrets
```bash
# Set your Telnyx API key as a secret on the Edge Compute function
telnyx-edge secret set TELNYX_API_KEY your_telnyx_api_key
```
Programmatic / CLI setup
```bash
# Buy a number (if you don't have one)
telnyx number-orders create --phone-number "+16282564655"
# Create a Call Control application
telnyx call-control-applications create \
--application-name "voice-agent-holds-call" \
--webhook-url "https://edge-voice-agent-holds-call-.telnyxcompute.com/webhooks/voice"
# Assign the number to the application
telnyx numbers update +16244444444 --connection-id
```