# Retell AI — A voice AI platform for human-sounding phone agents, build a call flow, plug in your model and telephony, ship.

> Source: The Agents Index — https://theagentsindex.com/retell-ai (structured, researched, re-verified)
> Facts last verified: 2026-07-23

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.

| Fact | Value |
| --- | --- |
| Website | https://www.retellai.com |
| API | Yes |
| Best for | Product and engineering teams that want a low-latency, human-sounding phone agent with flexible model and telephony choice. |
| Not for | Non-technical buyers wanting a fully no-code, hands-off turnkey product with white-glove support. |

## Verdict

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.

## Strengths and weaknesses

- ✓ Natural voice quality and low latency, with an easy-to-use interface, are the most-cited strengths in user reviews.
- ✓ Wide integration surface — Twilio, Salesforce, HubSpot, Zapier, Five9 and more — plus simulation testing and analytics.
- ✓ Capital-efficient, profitable growth is a real product-market-fit signal, not just funding hype: Retell reached $60M ARR by April 2026 (up ~650% year-over-year) while staying profitable with roughly 20-25 employees, on a single $4.6M seed round.
- ✓ Genuine, quantified enterprise outcomes across a broad customer base: Sunshine Loans scaled to 700,000+ monthly loan applications while cutting abandonment below 5%, and Medical Data Systems now processes $280,000/month in debt collections through Retell voice agents.
- ✗ Component-based pricing hides complexity: the $0.07/min headline climbs to roughly $0.13–$0.20+/min once you add a good LLM, quality voice, telephony, knowledge base and safety features.
- ✗ Developer knowledge is required, and some reviews report a limited visual builder and slow support responses.
- ⚠ True per-minute cost is the sum of stacked components, so budgeting requires modelling model + voice + telephony together.
- ⚠ It is developer-oriented — non-technical teams may find advanced flows and testing a steep learning curve.

## 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.

## 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.

## Integrations

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

## Sources

- https://www.retellai.com/pricing
- https://www.g2.com/products/retell-ai/reviews
- https://www.retellai.com/about-us
- https://www.retellai.com/blog/seed-announcement
- https://www.globenewswire.com/news-release/2026/01/29/3228780/0/en/Upgraded-Retell-AI-Voice-Platform-Enables-Corporate-Call-Centers-to-Deploy-Infinite-AI-Sales-and-Support-Agents-Across-Voice-Chat-Email-and-SMS-Company-Revenue-Now-Exceeds-40M-ARR.html
- https://sacra.com/research/retell-ai-60m-yr-up-650-yoy/
- https://www.retellai.com/customers
- https://docs.retellai.com/get-started/mcp-server