Retell

Freemium

voice aiconversational aiapideveloper toolsllmspeech-to-texttext-to-speechcustomer supportautomationtelephony

Retell AI is a powerful, developer-first API for creating impressively human-like voice agents, though its specialization means it's a component, not a complete out-of-the-box solution.

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An API for developers to build voice agents with sub-500ms latency that sound and feel remarkably human.

Retell AI provides a developer-focused API to create incredibly fast and lifelike conversational voice agents. The platform is engineered to solve the complex challenges of real-time voice interactions, such as handling interruptions and maintaining a natural conversational flow, achieving an end-to-end latency of under 500 milliseconds. It is designed for developers and businesses aiming to build sophisticated voice-based applications. Use cases range from automated customer support and appointment scheduling to intelligent sales outreach and interactive voice response (IVR) systems. By abstracting away the intricacies of conversational dynamics, telephony, and real-time transcription, Retell AI enables developers to connect any large language model (LLM) and focus purely on the agent's logic and purpose, resulting in more engaging and effective user experiences.

Pros

Extremely low latency enables natural, fluid conversations
Advanced conversational AI handles interruptions and turn-taking
Developer-friendly API simplifies complex voice AI development
Generous free tier for testing and small-scale projects
Flexible and model-agnostic, supporting various LLMs
High-quality, customizable voices

Cons

Usage-based pricing can be difficult to predict for high-volume needs
Requires development resources to implement; not a no-code tool
As a relatively new company, long-term roadmap is still evolving
Focused purely on voice; lacks built-in omnichannel features

Key features

Sub-500ms end-to-end latency for real-time conversation
Human-like conversation flow with interruption handling
Simple API to integrate with any application
Connects to any LLM backend (e.g., GPT, Claude, custom models)
Built-in telephony for PSTN and VoIP calls
Customizable voices, languages, and agent personas
Real-time transcription and speech recognition
Server-sent events (SSE) for low-latency streaming

Integrations

OpenAI GPT modelsAnthropic Claude modelsGoogle Gemini modelsGroqTwilioVercel AI SDKLangChainLlamaIndex

Target audience

Developers and businesses building conversational voice AI applications for customer service, sales, and support.

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Key Metrics

Founded

2023

Headquarters

San Francisco, USA

Pricing Tiers

Free

Pay As You Go - Standard

$0.04/min

Pay As You Go - Enhanced

$0.08/min

Pay As You Go - Premium

$0.12/min

Enterprise

Custom

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