Integrate Claude, Anthropic’s AI Assistant, with Twilio Voice Using Conversation Relay

Twilio published a tutorial for connecting Anthropic's Claude to Twilio Voice through Conversation Relay, a WebSocket-based service that links phone calls to an LLM provider of the user's choice. The guide has developers build a Node.js server on Fastify using Anthropic's TypeScript SDK, requiring Node.js 24+ (built on 24.22.0), a Twilio voice-capable number, an Anthropic API key, and Ngrok for tunneling. The tutorial instructs users to complete Conversation Relay onboarding in the Twilio Console under Communications > Voice > Settings > Privacy & Security, including the Predictive and Generative AI/ML Features Addendum, and uses a system prompt that avoids special characters and spells out numbers for text-to-speech.

Integrate Claude, Anthropic’s AI Assistant, with Twilio Voice Using Conversation Relay Time to read: Written by Reviewed by Integrate Claude, Anthropic’s AI Assistant, with Twilio Voice Using Conversation Relay introduction Twilio’s Conversation Relay https://www.twilio.com/docs/voice/twiml/connect/conversationrelay allows you to build real-time, human-like voice applications with AI Large Language Models LLMs that you can call using Twilio Voice https://www.twilio.com/en-us/voice . Conversation Relay connects to a WebSocket you control, allowing you to integrate the LLM provider of your choice over a fast two-way connection. This tutorial demonstrates a basic integration of Claude, Anthropic's AI model https://claude.com/product/overview , with Twilio Voice using Conversation Relay. By the end of this guide, you'll have a functioning Claude voice assistant powered by a Node.js server that lets you call a Twilio phone number and engage in conversation with an Anthropic model Prerequisites toc-heading-2b045f7f-3e91-4b46-b051-8a66d4d2b07a Prerequisites To deploy this tutorial, you'll need: - Node.js https://nodejs.org/en 24+ I used 24.22.0 to build this tutorial - A Twilio account you can sign up for free, here https://twilio.com/try-twilio and a phone number with voice capabilities - An Anthropic account https://platform.claude.com/login and API Key https://platform.claude.com/settings/keys - Ngrok https://ngrok.com/ or another tunneling solution to expose your local server to the internet for testing - A phone to place your outgoing call to Twilio - Your code editor or IDE of choice Before using Conversation Relay, you need to complete the onboarding steps and if you agree to the Predictive and Generative AI/ML Features Addendum, agree there. In the Twilio Console https://1console.twilio.com/ , go to Communications Voice Settings Privacy & Security. See the Conversation Relay Onboarding Guide https://www.twilio.com/docs/voice/conversationrelay/onboarding for more details. Great Let’s get started. Set up your project toc-heading-05290469-b178-455e-8a1f-c25981738964 Set up your project These next steps will cover project setup and the dependencies you’ll need to install. Then, you'll create the server code and I’ll explain the more interesting parts . Create the project directory toc-heading-a65da513-c310-4445-a124-bd750641beef Create the project directory First, set up a new project folder: Initialize the Node.js Project Next, initialize a new Node.js project and install the necessary packages: You'll be using Fastify https://fastify.dev/ to create a server that handles both the WebSocket needed for Conversation Relay and the endpoint for Twilio instructions required by Twilio Voice. You’ll use Anthropic’s Typescript library https://github.com/anthropics/anthropic-sdk-typescript to manage the conversation with Claude. Configure Environment Variables configure-environment-variables Create an .env file to store your Anthropic API key. Add the following line: Write the code toc-heading-f9fd21a0-59f4-48f8-a887-73d69dbfa113 Write the code Awesome, you’re really cooking now. Let’s move on to the server code. Create a file named server.js and add the following imports and constants: Here, you’ll notice we define our WELCOME GREETING . This is the first thing someone will hear when they dial into your assistant. You’ll also notice a SYSTEM PROMPT , which controls the behavior of the voice assistant. There, we let the LLM know some of our preferences for the conversation. This prompt asks the LLM to avoid special characters and asks it to write out numbers to make it easier for the Text-to-Speech step to work. Implement the AI response function In this next step, you will define how your app connects to the Anthropic API and handle responses. Paste this code below the above: Here, you add what we need to connect to Anthropic. process.env.ANTHROPIC API KEY will get our API key from the .env file to authenticate our usage of Anthropic, then the aiResponse function is what is used to control the behavior of each LLM response. For this demo, you will use claude-sonnet-5-5 at low effort to test the build. You can find Anthropic’s supported Claude models in their documentation https://platform.claude.com/docs/en/models/overview . Configure Fastify, and set up routes Now that you've defined your interactions with Claude, it's time to move on to Twilio. You're going to set up two endpoints in this step: - /twiml - to control Twilio’s behavior when we make an incoming call to our purchased number. This uses Twilio Markup Language, or TwiML https://www.twilio.com/docs/voice/twiml , to instruct Twilio further. - /ws - for a WebSocket connection that Conversation Relay will use to communicate with your application. Here you will receive messages from Twilio, but you will also need to pass messages from your LLM back to Twilio to trigger the Text-to-Speech step the relay , if you will . Below the code from the above step, paste the following: And that’s all the code you need for a basic integration – now, let’s get everything running and connect it to Twilio Start ngrok and the server toc-heading-5bb77c22-bc0d-4c22-97c4-4aecc24abc46 Start ngrok and the server Open a terminal or a new terminal tab and start ngrok with ngrok http 8080 . There, copy the ngrok URL without the scheme that is, leave out the “https://” or “http://” and update your .env file by adding a new line: This screenshot shows the URL I chose for my environment variable: Finally, start your server. In the original terminal not the one running ngrok , run: Configure Twilio configure-twilio In the Twilio Console https://console.twilio.com/ , configure your phone number with the Voice Configuration Webhook for A call comes in set to https:// your-ngrok-subdomain .ngrok.app/twiml . Here’s an example from my Console: Save your changes, you’re now ready to test. Test your integration Are you giddy with anticipation? It’s time Call your Twilio number. The AI should greet you with the WELCOME MESSAGE and be ready for a conversation – be sure to ask it for owl jokes Next steps with Twilio and Claude I hope you enjoyed this basic integration of Twilio Voice with Anthropic’s Claude using Conversation Relay – dial-a-voice-LLM in under 100 lines of code You’ll probably want to add more advanced features next. Our follow-up article shows you how to stream tokens from Anthropic to Conversation Relay to reduce latency https://www.twilio.com/en-us/blog/anthropic-conversationrelay-token-streaming-interruptions-javascript , as well as how to better handle interruptions by tracking your conversation locally. And after that, I’ll show you the basics of how to call tools or functions with Claude using Conversation Relay https://www.twilio.com/en-us/blog/developers/tutorials/product/function-calling-twilio-voice-anthropic-claude-integration . But until then, have fun with the scaffolding… check out Twilio’s Conversation Relay docs https://www.twilio.com/docs/voice/twiml/connect/conversationrelay , Anthropic’s API documentation https://platform.claude.com/docs/en/api/overview , and Anthropic’s TypeScript SDK https://github.com/anthropics/anthropic-sdk-typescript to learn more. Paul Kamp is the Technical Editor-in-Chief of the Twilio Blog. He was excited to talk to the LLM about recipes… but a bit disappointed he only found time to cook a few suggestions when will agents make food? . Reach Paul at pkamp at twilio.com. Related Posts Related Resources Twilio Docs From APIs to SDKs to sample apps API reference documentation, SDKs, helper libraries, quickstarts, and tutorials for your language and platform. Resource Center The latest ebooks, industry reports, and webinars Learn from customer engagement experts to improve your own communication. Ahoy Twilio's developer community hub Best practices, code samples, and inspiration to build communications and digital engagement experiences.