By Sagar Shankaran, Founder of CallSphere
Build a voice agent that runs entirely on Cloudflare's edge: Calls SFU for WebRTC, withVoice mixin for STT/TTS, Workers AI for inference. No external infra, sub-300ms hops.
Key takeaways
TL;DR — Cloudflare's Agents SDK now ships
withVoice, a mixin that adds STT (Deepgram Nova/Flux), sentence chunking, TTS (Aura), and conversation persistence to a regular Agent class. Combined with Cloudflare Calls (their WebRTC SFU) and Workers AI, you get an end-to-end voice agent on the same edge network — no external API keys for the happy path.
A @cloudflare/voice-powered Agent deployed to Workers, with audio transported over WebSocket from a browser client. The agent uses Workers AI's Llama 3.3 70B for reasoning, Deepgram Flux for streaming STT, and Aura for TTS — all bound natively. Optional: hand the WebSocket to Cloudflare Calls for browser-to-browser group voice rooms with the AI as a participant.
wrangler@4 CLI authenticated.flowchart LR
B[Browser React] -->|wss| AGT[Worker Agent withVoice]
AGT -->|STT| DG[Deepgram Flux Workers AI]
AGT -->|LLM| WA[Workers AI Llama 3.3 70B]
AGT -->|TTS| AU[Deepgram Aura]
AGT --> B
B <-->|WebRTC SFU| CALLS[Cloudflare Calls]
```bash npm create cloudflare@latest voice-agent -- --type=workers-ai cd voice-agent npm install @cloudflare/voice agents ```
```ts // src/agent.ts import { Agent } from "agents"; import { withVoice } from "@cloudflare/voice";
export class Receptionist extends withVoice(Agent) { async onChatMessage(message: string) { const reply = await this.env.AI.run("@cf/meta/llama-3.3-70b-instruct-fp8-fast", { messages: [ { role: "system", content: "You are a friendly receptionist. Keep replies short." }, { role: "user", content: message } ] }); return reply.response; } } ```
The withVoice mixin handles audio in/out automatically; you only implement onChatMessage(text).
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```toml name = "voice-agent" main = "src/index.ts" compatibility_date = "2026-05-01"
[ai] binding = "AI"
[[durable_objects.bindings]] name = "RECEPTIONIST" class_name = "Receptionist"
[[migrations]] tag = "v1" new_sqlite_classes = ["Receptionist"] ```
```ts import { Receptionist } from "./agent"; export { Receptionist }; export default { async fetch(req: Request, env: Env) { const url = new URL(req.url); if (url.pathname === "/voice") { const id = env.RECEPTIONIST.idFromName(url.searchParams.get("session") ?? crypto.randomUUID()); return env.RECEPTIONIST.get(id).fetch(req); } return new Response("ok"); } }; ```
```tsx import { VoiceClient } from "@cloudflare/voice/client"; const client = new VoiceClient({ url: `wss://voice-agent.you.workers.dev/voice?session=${crypto.randomUUID()}`, inputSampleRate: 16000, outputSampleRate: 24000, }); await client.start(); ```
The client handles getUserMedia, AudioWorklet capture, WS framing, and Web Audio playback.
In Receptionist.constructor:
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```ts super(state, env, { voice: { stt: { provider: "deepgram-flux", model: "flux", language: "en" }, tts: { provider: "deepgram-aura", voice: "aura-asteria-en" }, vad: { silenceThresholdMs: 500 } } }); ```
If you want the AI to join a multi-party WebRTC room (caller + AI + supervisor), use Cloudflare Calls' SFU API to publish/subscribe tracks. The agent's withVoice audio output becomes a track published into the SFU room; humans subscribe via standard WebRTC.
fetch("https://rtc.live.cloudflare.com/v1/apps/{appId}/sessions/new", { method: "POST", headers: { Authorization: \Bearer ${env.CALLS_TOKEN}` } })`
withVoice mixin runs inside a Durable Object so this isn't a problem, but plain Workers wouldn't work.Promise.race against a smaller model (8B) for first-token TTS.Nova is batch and adds 200ms.withVoice expects PCM16 mono; resample on the client if your mic capture differs.CallSphere doesn't deploy the voice path on Cloudflare Workers because our HIPAA Healthcare vertical needs Postgres-resident audit logs that fit our 115+ table schema. We do use Cloudflare in front of FastAPI :8084 as a CDN + DDoS layer, and we've experimented with Workers AI for the OneRoof multi-family vertical's chat fallback. 37 voice agents, 90+ tools, 6 verticals, $149/$499/$1499, 7-day free pilot, 22% affiliate.
Q: How do I add my own STT/TTS provider?
withVoice accepts stt: { provider: "custom", run: async (pcm) => string }. Plug in OpenAI Whisper, Azure, anything.
Q: Can I use Workers AI alone without Deepgram?
Yes — Workers AI ships @cf/openai/whisper-large-v3-turbo for STT and @cf/myshell-ai/melotts for TTS. Quality is lower than Deepgram on Aura but free under the binding.
Q: Latency target? ~500-700ms voice-to-voice on Cloudflare's network because everything is colocated. The win vs other clouds is no inter-service hops.
Q: PSTN?
Twilio Media Streams as a SIP frontend; the Worker handles the Media Stream WS and translates frames to withVoice's expected format.
Q: Cost?
Workers AI Llama 3.3 70B is $0.4 per 1M input tokens, $0.6 per 1M output. Deepgram Flux STT is included in the @cloudflare/voice binding pricing — call it $0.005/min STT + $0.012/min TTS + $0.02/min LLM = ~$0.04/min all-in.
Written by
Sagar Shankaran· Founder, CallSphere
LinkedInSagar Shankaran is the founder of CallSphere, where he builds production AI voice and chat agents deployed across healthcare, hospitality, real estate, and home services. He writes about agentic AI, LLM engineering, and shipping voice agents that handle real calls in production.
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