Retell AI

What is Retell AI?

Retell AI is a platform for building AI voice agents that handle inbound and outbound phone calls. It combines a conversational agent framework with a proprietary turn-taking and voice-orchestration layer aimed at low-latency, human-sounding calls, and lets teams pick their language model, voice and telephony provider. Agents can answer support questions, qualify leads, book appointments and update business systems in real time, and are deployable over the phone, chat, SMS or an API. Founded in 2023 by five co-founders — Bing Wu (CEO), Zexia Zhang (CTO), Todd Li (President), Weijia Yu (COO) and Evie Wang (CMO) — Retell went through Y Combinator’s Winter 2024 batch, launched publicly in February 2024, and closed a $4.6M seed round led by Alt Capital later that year, with participation from Y Combinator and angels including Box CEO Aaron Levie. It has grown quickly since on that modest raise, reaching $60M in annualized revenue by April 2026 (up roughly 650% year over year from $40M+ ARR at the end of 2025) while staying profitable with a team of around 20-25 people.

What does Retell AI do?

You build an agent in Retell’s dashboard — configuring a prompt or a multi-step conversation flow, connecting a knowledge base, and defining functions the agent can call — then deploy it to a phone number or embed it via the API. On a live call Retell orchestrates transcription, the LLM and text-to-speech with roughly ~600ms latency, using its own turn-taking model to decide when to speak versus listen. Agents can call custom functions mid-call to fetch data or take actions, stream answers from an auto-syncing RAG knowledge base, transfer calls to humans, and run outbound campaigns via batch calling. It supports SIP trunking so you can bring existing numbers, plus branded caller ID and verified numbers. After each call, Retell provides transcripts, post-call analysis and analytics, and an AI quality-assurance layer that simulates conversations to test agents before they go live. It is developer-oriented but ships templates and a builder to shorten setup.

Key features

• Conversation flow builder: A drag-and-drop agentic framework with guardrails for designing multi-step call flows, IVR trees and dynamic transfers.
• Low-latency voice engine: A proprietary turn-taking model targets ~600ms latency for natural back-and-forth on calls.
• Streaming RAG knowledge base: Agents answer from an auto-syncing knowledge base and call real-time functions to fetch data or act.
• Batch calling + AI QA: Run outbound campaigns at scale and simulation-test agents against edge cases before going live.

What are Retell AI's use cases?

• Inbound support & booking: An agent answers questions, books appointments and updates the CRM in real time, transferring to a human when needed.
• Outbound campaigns: Batch calling runs lead-qualification or reminder campaigns from imported numbers with branded caller ID.

What does Retell AI integrate with?

• Telephony — Twilio, Vonage, Telnyx
• CRM — Salesforce, HubSpot, GoHighLevel
• Automation — Zapier, n8n, Make, Cal.com
• Contact centres — Five9, Amazon Connect, Nice, Talkdesk
• Model Context Protocol (MCP) — both an MCP server (build/manage Retell agents from MCP-capable clients) and mid-call MCP client tool calls

Why use Retell AI?

• Strong voice quality and low latency that users consistently praise for real-world call handling.
• Flexible stack — choose your LLM, voice and telephony provider rather than being locked to one.
• Broad telephony/CRM integrations plus built-in simulation testing and post-call analytics.

Pros & cons

Retell AI pricing

• Pay-as-you-go$0.07–$0.31 / /min
• EnterpriseCustom

See current pricing on retellai.com ↗Compare Retell AI alternatives →

Retell AI review

Retell AI is one of the strongest developer-first voice platforms, and its reputation rests on the two things that matter most on a phone call: natural voice quality and low latency, backed by a proprietary turn-taking model at around 600ms. You assemble the stack — LLM, voice, telephony — and get a real builder, an auto-syncing knowledge base, batch calling and simulation testing, plus a broad set of CRM and contact-centre integrations. The trade-offs are the usual ones for this class: component pricing that starts at $0.07/min but realistically lands north of $0.13–$0.20/min once fully specced, and a learning curve that assumes technical staff. Pick Retell if you want top-tier voice quality with control over the stack; skip it if you need a no-code tool with predictable flat pricing and hands-on support.

A voice-quality leader for technical teams — excellent calls, but price it fully-loaded, not off the $0.07/min headline.

Frequently asked questions