Build voice AI into your application
You already have a product. Add a real-time voice layer to it without building the speech pipeline yourself. Plug voice in through a phone number, a browser call, or your API, and keep every transcript and outcome in your own systems.
Skip the part that takes months
Adding voice from scratch means stitching speech recognition, a language model, a natural voice and telephony into one loop that answers in under a second, handles interruptions, and stays up under real traffic. Teams lose months there, and the maintenance never ends. Nixflex runs that whole engine and hands you a clean surface to build against, so the work becomes an integration, not an infrastructure project.
Three ways voice plugs into your product
Attach a number to an agent
Point one of your own Twilio or Telnyx numbers at an agent and it answers and places calls immediately. Cold and warm transfers, SMS, and voicemail handling come with it. One agent template can sit behind many numbers.
Voice in the browser
Start a web call from your frontend and the user talks to the same agent right inside your app, with no phone number involved. It is the quickest way to add a talk-to-it experience where a user is already signed in.
Drive it from your backend
Create agents, attach numbers, place calls and read results over one REST API, and receive webhook events as calls happen. Your server stays in control, and the agent can call back into your API mid-conversation through custom functions.
The data lands in your systems
A voice feature is only useful if what it captures reaches the rest of your product. Every call returns a transcript, a summary and a sentiment score, with any fields you asked the agent to extract, pushed to your webhook the moment a call ends or pulled from GET /v1/calls. Nothing is trapped in a dashboard. It flows to the CRM, database or queue your app already runs on.
Plain REST, from any language
There is no SDK to adopt before you can start. Nixflex is a REST API, so you call it from whatever language your product is written in, with the HTTP client you already use. Typed client libraries are on the roadmap, but the endpoints and payloads in the docs are exactly what you call today, with no wrapper in between.
See the full surface in the docs, or the Voice AI API and Web Call API pages. Coming from another platform? Nixflex is a modern alternative to Retell, Vapi and Bland. Compare them →
Developer FAQ
How do I add voice to an app I already have?
Pick the surface that fits. To answer phone calls, attach one of your carrier numbers to an agent. To put voice in your web app, start a browser call from your frontend. To drive everything from your backend, use the REST API and receive webhooks. You do not rebuild your product; voice plugs into the surface you already have.
Do I have to build the speech pipeline myself?
No, and that is the point. Wiring speech recognition, a language model, a voice and telephony into one low-latency loop, then keeping it alive under load, is weeks of work that never quite ends. Nixflex runs that pipeline on its own engine and gives you a REST interface, so you integrate in hours instead of building infrastructure for months.
Can I keep the conversation logic in my own code?
Yes. The agent handles the call, but during a conversation it can call your API through custom functions, so your business logic stays in your codebase. The engine supplies anything that has to be exact, like a date or a reference number, rather than leaving the model to guess.
Does the call data come back into my systems?
Yes. Every call returns a transcript, summary and sentiment, pushed to your webhook as events or pulled from GET /v1/calls. Nothing is locked in a dashboard you have to log into; the data lands where your product can use it.
Can I put voice in the browser, not just on the phone?
Yes. Web calls run voice directly in your web app over the browser, with no phone number involved, using the same agent. It is the fastest way to add a talk-to-it experience inside a product a user is already logged into.
Will it scale with my product?
Yes. One agent is a template that attaches to unlimited numbers, and calls run concurrently, so adding customers is adding numbers, not re-architecting. Provider failover for speech, model and voice is built in, so a single vendor blip does not take your feature down.
What does it cost to add?
A flat $0.08 per minute of voice, pay-as-you-go, premium model included, with your own carrier underneath. No credits, no per-feature upcharges, and no monthly platform fee to start, so the cost of the feature is predictable from the first call.
Add voice to your app this week
Pick a surface, wire it in, and keep the data where your product needs it.