Glossary · AI & Agents
Retell AI
Overview
What Retell AI is
Retell AI is a platform for building and running AI voice agents that talk on the phone. It provides the infrastructure layer, speech pipeline, telephony integrations, and orchestration needed to automate live phone conversations without stitching those pieces together yourself.
It targets both developers, through APIs and SDKs, and less technical teams, through a drag-and-drop conversation builder. Common uses include lead qualification, appointment booking, customer support, and routine transactions like FAQs.
How it works
You bring your own telephony or use Retell's, connect a large language model, and design a call flow. When a call happens, incoming speech is transcribed, the model decides how to respond based on your flow and connected tools, and the reply is spoken back with sub-second latency.
Retell integrates with telephony providers such as Twilio, supports multiple languages and voices, and can trigger webhooks or call functions to check calendars, update a CRM, or fetch data mid-conversation.
When to use it
Retell AI fits businesses that want production phone agents quickly without building the real-time voice stack from scratch. It is a strong choice for call-heavy workflows like reception, booking, and after-hours coverage.
It is one of several managed voice platforms; Vapi is a close alternative, and LiveKit is the open-source route for teams that want to own the infrastructure. Pricing is usage-based, so per-minute costs and included telephony should be checked against expected call volume.
Where we use it
Related Zen in Tech services
How our team puts Retell AI to work in real projects.
FAQ
Retell AI — common questions
What does Retell AI do?
Retell AI builds AI voice agents that make and receive phone calls. They handle tasks like qualifying leads, booking appointments, answering common questions, and routing callers, using natural speech with low latency.
Does Retell AI need coding?
Not necessarily. Retell offers a drag-and-drop builder for designing call flows without code, alongside APIs and SDKs for developers who want deeper control and custom integrations.
How is Retell AI different from Vapi?
Both are managed platforms for AI phone agents with similar STT-LLM-TTS pipelines. Retell leans toward an approachable builder plus API, while Vapi is positioned as a developer-first platform; the best fit depends on how much you want to build versus configure.
Need Retell AI done right?
Book a free consultation and we’ll map the fastest, most cost-effective path for your project.
Knowledge hub
From our knowledge hub
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