You want an AI that can pick up a call or sit inside your app and actually talk with people in real time. It should listen, answer out loud, and let people cut in.
The OpenAI Realtime API is one well-known way to build that, but it is far from the only path, and the right choice depends on where your conversations happen.
So, this guide walks you through 3 strong alternatives for 2026: Telnyx, Google Gemini Live API, and Deepgram Voice Agent API. You will see how each one builds a live conversation, where it fits best, and what to keep in mind before you commit.
TL;DR
Telnyx: best for teams that want OpenAI's GPT-Live speech-to-speech voice on phone calls, or a voice pipeline built from models they pick, with phone numbers and tools kept in one place.
Google Gemini Live API: best for apps where one model should hear, speak, and look at camera frames in the same live conversation.
Deepgram Voice Agent API: best for builders who want the full listen, think, and speak loop behind one connection, with the freedom to choose and swap the AI model and voice.
In short, Telnyx can run GPT-Live or an assistant you build yourself right on phone lines, with tools in the same place; Gemini Live keeps everything inside one model that hears and sees; and Deepgram gives you a flexible pipeline you can rewire during a call.
What Counts As An OpenAI Realtime API Alternative?
The OpenAI Realtime API lets an app talk with people out loud, in real time. It works with audio directly, remembers what has been said, and can use tools, whether people reach it from a browser, an app, or a phone call.
Still, some teams want their own AI model, built-in phone numbers, or an AI that can see through a camera. Therefore, a real alternative should be able to:
Hear and answer live, without an awkward pause.
Handle interruptions and recognize when someone has finished a thought.
Call tools and take actions without leaving the caller in silence.
Reach people on a web page, in a mobile app, or on an ordinary phone number.
So, a strong option covers all four.
The 3 below do, though Gemini reaches phone lines through partners, and each one builds the conversation in its own way.
The Top 3 Options Side By Side
1. Telnyx
Telnyx is a natural fit if you like the feel of OpenAI's speech-to-speech voice but want it working on real phone calls, next to your own tools and models.
It can host OpenAI's GPT-Live, a full-duplex speech-to-speech model, which simply means it listens and talks at the same time, inside a Telnyx voice assistant that runs on your own OpenAI key. Moreover, if you prefer, the same assistant can be built from separate listening, thinking, and speaking engines instead.
How It Handles Live Conversations
Speech-to-speech with GPT-Live: Because GPT-Live hears and speaks in one model, callers can talk over it without breaking the rhythm. You can run it inside a Telnyx assistant, or route a Telnyx phone number straight to it over an encrypted SIP connection.
Tool work handed to a back-end model: GPT-Live can't call tools on its own, so Telnyx pairs it with a second model behind the scenes. While GPT-Live keeps chatting, that model runs the lookups and actions, a setup currently in beta.
A pipeline you assemble: If you skip GPT-Live, you can pick the listening engine yourself, such as Deepgram Flux or AssemblyAI, and voices from providers like ElevenLabs or MiniMax.
Live audio for apps and browsers: Apps can stream microphone audio to an assistant and get spoken replies back, with interruptions handled on the server, and a browser library handles the microphone and playback on web pages.
Pros
Runs OpenAI's GPT-Live speech-to-speech voice on your own OpenAI key.
Keeps phone numbers, SIP, and the voice assistant in one place.
Hosted AI models work with OpenAI's code libraries after a base URL and key change.
Lets an assistant think with any model that follows OpenAI's chat format, such as Azure OpenAI or AWS Bedrock.
Passes callers between specialist assistants with context intact.
Remembers returning callers across sessions.
Things To Keep In Mind
The base URL swap works for Telnyx's hosted AI models, not for live voice. So, you build your voice agent as a Telnyx assistant instead of reusing OpenAI Realtime code as-is. GPT-Live assistants also stick to OpenAI's own voices, run on your OpenAI account, and don't support backup models or workflows.
2. Google Gemini Live API
Gemini Live API is Google's way to hold a live, spoken conversation with Gemini.
A single native-audio model listens to a continuous stream of sound and answers in speech of its own, with no separate transcription or voice step in between. So, the exchange feels like one continuous conversation rather than a relay between different engines.
How It Handles Live Conversations
Natural interruptions: Gemini stops talking the moment someone cuts in and drops any pending tool calls.
Tools and search in the same session: Gemini can call your functions and ground its answers with Google Search as it talks.
Video alongside voice: It sees camera video as still frames, up to about one per second.
Longer conversations: Sessions have time limits, but compression and resumption keep longer chats going.
Pros
Hears, speaks, and sees camera frames in one live conversation.
Uses a single model, so there is no hand-off between separate speech engines.
Suits helpers that talk someone through whatever is in front of their camera.
Adjusts its tone to match how a person sounds.
Switches languages mid-conversation across a wide range of languages.
Things To Keep In Mind
The Live API is still in preview on Google's developer API, while its live models are generally available on Google Cloud. Google Cloud also lets you protect saved session data with your own encryption key. And finally, Gemini has no phone network of its own, so calls come in through partners such as Twilio, Voximplant, Daily, or LiveKit.
3. Deepgram Voice Agent API
Deepgram Voice Agent API puts the whole listen, think, and speak loop behind one live connection.
Speech recognition, the AI model, and the voice all run together, with end-of-turn detection, interruptions, and tool calling already built in. Therefore, you get the flexibility of a pipeline without wiring three separate services together yourself.
How It Handles Live Conversations
Smarter turn-taking: Deepgram's Flux listening model decides when the caller has finished speaking, and the agent can prepare a reply early but holds it back until the turn is confirmed.
Your choice of brain: You can use managed models from OpenAI, Anthropic, Google, or NVIDIA, or bring your own through Groq, Amazon Bedrock, or any endpoint that follows OpenAI's chat format.
Safer actions: Tools can run in your app or on the server, and irreversible actions, such as hanging up, can wait until the caller has truly finished speaking.
Backup voices: You can list voice providers in order, so if one fails, speech moves to the next one automatically.
Pros
Handles listening, thinking, and speaking behind one connection.
Swaps the AI model, prompt, and tools mid-call without rebuilding the voice path.
Lets you choose managed models from OpenAI, Anthropic, Google, or NVIDIA, or bring your own.
Switches to a backup voice provider automatically if one fails.
Runs fully managed, single-tenant, in your own private cloud, or self-hosted.
Things To Keep In Mind
The automatic backup covers voices only. If you want a different AI model mid-call, you switch it yourself. Sessions also end after about two hours, though you can pick up again by replaying earlier turns, and phone calls come in through partners such as Twilio, Genesys, Amazon Connect, and AudioCodes.
So, Which Realtime Voice Option Fits You?
There is no single winner here, only the option that matches how your conversations actually happen. Once you know where people reach you, the choice gets much clearer.
Choose Telnyx if your agent lives on phone calls and you want OpenAI's GPT-Live voice, or a pipeline of your own picks, working alongside OpenAI-compatible hosted models and your phone numbers.
Choose Google Gemini Live API if your app needs one model that hears, speaks, and looks at camera frames in the same conversation.
Choose Deepgram Voice Agent API if you want one connection for the whole voice loop and the freedom to rewire the AI model, prompt, and tools mid-call.
