Build Voice AI Apps: A Guide to the Real Time Agent API in 2026

Bolti, a voice AI platform for building production-ready conversational phone agents, provides a robust developer interface for building low-latency, conversational voice systems. Whether you are automating outbound sales, customer support, or HR candidate screening, you can get started quickly with a 50-minute free trial to test your integration.

Building with voice requires handling complex audio pipelines under tight latency budgets. A dedicated developer API abstracts away the low-level complexities of speech processing so you can focus on agent behavior and business logic.

What is a real time agent api?

A real time agent api is a programming interface that allows developers to programmatically configure, initiate, and manage live voice conversations between humans and AI agents. It handles the orchestration of real-time speech-to-text (STT), large language models (LLMs), and text-to-speech (TTS) engines.

Instead of manually managing raw audio streams, web sockets, and voice activity detection (VAD), developers use a unified API to trigger calls, pass dynamic context, and receive structured webhooks. This lets your backend systems control exactly when a call happens and what information the AI agent possesses at the start of the conversation.

Under the hood of the voice pipeline

Every call initiated through the Bolti runtime runs a continuous loop many times per second to ensure a natural, human-like conversation. Understanding this flow is key to designing effective API integrations:

• Speech-to-Text (STT): Transcribes the caller's audio in real time using high-performance providers like Deepgram or AssemblyAI.
• Voice Activity Detection (VAD) & Turn Detection: Determines exactly when a caller starts and stops speaking, resolving the natural pauses in human speech.
• Large Language Model (LLM): Processes the transcribed text alongside your system prompt, dynamic context, and available tools to generate the next response.
• Text-to-Speech (TTS): Synthesizes the generated response into high-fidelity audio using providers like Cartesia, ElevenLabs, or SarvamAI.
• Interruption Handling: Continuously monitors for incoming audio streams, allowing the user to cut off the AI agent mid-sentence, just like a real phone call.

All of these components are packaged into a single agent entity that you can provision and trigger with a single API request.

How to trigger outbound calls programmatically

To place an outbound call, your system makes a simple HTTP request to the runtime endpoint. You must specify the agent configuration to use, the destination phone number, and the outbound caller ID.

Here is how you can initiate an outbound call using a standard REST request:

POST /workspaces/{workspace_id}/agents/{agent_id}/outbound-call
Authorization: Bearer <your_api_token>
Content-Type: application/json

{
  "to_number": "+919876543210",
  "from_number": "+912212345678",
  "dynamic_context": {
    "customer_name": "Amit Sharma",
    "outstanding_balance": "₹2,450"
  }
}

When this request is received, Bolti spins up a real-time call room, dials out via your connected telephony provider (such as Twilio, Exotel, or Plivo), and connects the audio to the active agent worker.

Managing agent configurations via API

An agent is the core unit of deployment. You can create, retrieve, and update agent behaviors programmatically. This is particularly useful if your application dynamically generates custom system prompts or custom instruction sets based on user actions.

POST /workspaces/{workspace_id}/agents
Authorization: Bearer <your_api_token>
Content-Type: application/json

{
  "name": "Support Agent",
  "language": "hi-IN",
  "system_prompt": "You are a helpful customer support assistant for a retail company...",
  "voice_provider": "cartesia",
  "voice_id": "english-male-1"
}

Because agents are the unit of deployment, any updates you push via the API apply instantly to the next call. In-flight calls will continue running on their old configuration, eliminating the need for complex redeployment scripts or server restarts.

Real-world use cases for voice APIs

Integrating voice agents directly into your application workflow opens up several automated communication channels:

• HR Screening Funnels: Automatically trigger phone screens when a candidate applies. You can read more about setting up these pipelines on our Bolti use cases page.
• Payment Reminders: Programmatically call customers with overdue invoices, state their balance dynamically, and collect payment confirmation.
• Appointment Booking: Connect incoming customer calls directly to an AI agent that can read your calendar, book slots, and write details back to your database using HTTP tools.

To understand how these call minutes are metered and billed, you can review our transparent pricing model on the Bolti pricing page.

Set up your first voice agent

You can build, test, and deploy a fully functional conversational voice agent in less than 10 minutes. Bolti offers ₹6/minute pay-as-you-go pricing with no hidden platform fees, as well as a free trial loaded with 50 minutes of call time so you can run complete end-to-end integration tests.

Create your developer account and start your free trial today to get your API keys and build your first real-time voice agent.

Frequently Asked Questions

What is the latency of the real time agent api?

Bolti is built for production phone calls with sub-second turn-taking latency. By streaming speech-to-text, LLM generation, and text-to-speech concurrently, the agent can begin speaking almost immediately after the caller finishes their sentence.

Can I bring my own telephony provider?

Yes. Bolti supports Bring Your Own Carrier (BYOC). You can register your own SIP trunks or connect existing accounts from providers like Twilio, Plivo, Exotel, or Vobiz directly in the dashboard or via the API.

How are changes to agent prompts deployed?

Agents are the unit of deployment. Any changes made to an agent's prompt, tools, or pipeline settings via the API or dashboard apply instantly to the very next call. Ongoing, active calls will finish using their original configuration.

Does the API support multiple languages?

Yes. Bolti supports over 80 global languages and regional Indian dialects, including Hindi, Marathi, Tamil, Telugu, Bengali, Gujarati, and English. You can configure the STT, LLM, and TTS settings per agent to match your target audience.