Retell AI

What is Retell AI?

Retell AI is a developer-friendly platform for building AI voice agents that hold natural phone conversations and carry out tasks during the call. You design the agent in a drag-and-drop flow builder or through the API, choose a language model and voice, connect a phone number and then let it handle inbound or outbound calls. The company quotes a response latency of about 600 milliseconds and also offers SMS and chat agents.

Retell AI was founded in 2023 in San Francisco and went through Y Combinator’s Winter 2024 batch, with Todd Li, Evie Wang, Bing Wu, Weijia Yu and Zexia Zhang listed as founders. It holds a 4.8 out of 5 rating from 2,638 reviews on G2. In October 2026 the platform was live with usage-based pricing, $10 of free credit and custom Enterprise contracts.

Key Features

• Visual agent builder: Retell AI provides a drag-and-drop flow builder for designing call logic without heavy coding. Developers can also build agents through the REST API and SDKs when they need full control.
• Low-latency voice: Retell AI states a response time of about 600 milliseconds, which keeps conversations from feeling stilted. Callers can interrupt, and the agent adjusts mid-sentence rather than finishing a script.
• Choice of models and voices: Retell AI lets you pick the language model per agent, from GPT 5 nano at $0.0016 a minute to GPT 5.5 at $0.16. Voices range from Retell’s own at $0.015 a minute to ElevenLabs v3 at $0.10.
• Call transfer and live monitoring: Retell AI transfers calls from the agent to a human when needed and lets supervisors listen in. Staff can step into a live call if the agent struggles with a request.
• Appointment booking: Retell AI checks calendar availability and books appointments during the call, with Cal.com among its listed integrations. Clinics, salons and service firms can take bookings outside office hours.
• Knowledge bases: Retell AI agents can draw on your existing documents while they talk, costing $0.005 a minute. Ten knowledge bases are included, and each extra one costs $8 a month.
• Batch outbound calls: Retell AI runs high-volume outbound campaigns for reminders, lead qualification or collections. The agent can also detect and navigate IVR keypad menus when it reaches another company’s phone system.
• Post-call analytics and QA: Retell AI analyses calls after they end and offers AI quality assurance across every call. QA costs $0.10 a minute, with the first 100 minutes free.
• Compliance add-ons: Retell AI offers PII removal, safety guardrails and advanced denoising as paid per-minute options. The company says it is SOC 2 Type II certified and HIPAA compliant, with GDPR and ISO 27001 alignment.

Pros

• Strong user ratings: Retell AI scores 4.8 out of 5 from 2,638 reviews on G2 in October 2026. That is a large review base for a company founded only in 2023.
• Natural conversations: Retell AI keeps response times near 600 milliseconds and handles interruptions well. Callers are less likely to hang up on an agent that responds like a person.
• No minimum spend: Retell AI starts on a pay-as-you-go plan with no contract and $10 of free credit. Small teams can build and test an agent before paying anything.
• Flexible model choice: Retell AI lets you swap language models and voice providers per agent. You can trade cost against quality, using a budget model for simple routing and a premium one for complex calls.
• Wide telephony support: Retell AI works with Twilio, Vonage and SIP trunking, so you can keep existing numbers and carriers. It also connects to Make, n8n, HubSpot, GoHighLevel and Cal.com.
• Enterprise compliance: Retell AI states SOC 2 Type II certification and HIPAA compliance, with SSO and role-based access. Healthcare and financial firms get controls they usually need before deploying voice AI.

Cons

• Hard-to-predict costs: Retell AI bills each minute as a stack of voice, model, voice provider, telephony and add-on charges. The total ranges from about $0.07 to $0.31 a minute, which complicates budgeting at scale.
• Learning curve: Retell AI suits teams with some technical skill more than non-technical users. One review cites more than 80 G2 reviewers mentioning a steep learning curve for complex agents.
• Extra monthly fees: Retell AI charges $2 a month per phone number and $8 per extra concurrent call above the 20 included. Verified numbers cost $10 a month each, which adds up for multi-location firms.
• Voice, SMS and chat only: Retell AI focuses on voice, SMS and chat, with no native email or LinkedIn outreach. Sales teams running multi-channel sequences need separate tools alongside it.
• Premium models cost more: Retell AI’s best-sounding voices and strongest models raise per-minute costs sharply. ElevenLabs v3 voices cost $0.10 a minute against $0.015 for Retell’s own platform voices.

Who is Using Retell AI?

• Healthcare clinics: answer patient calls and book appointments around the clock.
• Sales and lead-generation teams: qualify inbound leads and run outbound call campaigns.
• Contact centres: automate routine calls and transfer complex ones to staff.
• AI voice agencies: build and resell custom phone agents for clients.

Pricing

Retell AI charges per minute with no monthly minimum, with voice agents costing about $0.07 to $0.31 a minute and $10 of free credit for new accounts (official prices, October 2026).

G2 lists Enterprise contracts starting at $8,000, a figure we did not see on Retell’s own pricing page. Add-ons such as knowledge bases, PII removal and AI quality assurance each add a per-minute charge, so model your expected call minutes before you launch a campaign.

What Makes Retell AI Unique?

Retell AI gives you an unbundled voice stack where you pick the language model, voice and carrier for each agent and pay only for the minutes used. That makes it closer to infrastructure than a packaged call centre product, yet the drag-and-drop builder, live call monitoring and built-in QA keep it usable for operations teams. Its review volume on G2 is large for a 2023 start-up, which gives buyers more real-world evidence than most voice AI rivals offer.

Compatibilities and Integrations

• Telephony: Twilio, Vonage and SIP trunking, plus Retell’s own phone numbers.
• Automation and CRM: Make, n8n, HubSpot and GoHighLevel connections.
• Scheduling: Cal.com and calendar availability checks for bookings.
• API: REST API, SDKs and webhooks for custom builds and data export.

Retell AI Tutorials

A first Retell AI test call can be running within an hour.

1. Sign up at retellai.com and claim the $10 free credit.
2. Create an agent in the flow builder and choose the language model and voice.
3. Add a knowledge base and connect Cal.com or your CRM if the agent needs to book or log data.
4. Buy a Retell number or connect Twilio, Vonage or SIP, then place a test call.
5. Review the post-call analysis, refine the prompts and set concurrency before going live.

How We Rated It

Summary

Retell AI suits businesses and agencies that want natural-sounding phone agents and are comfortable configuring models, voices and carriers. Its main limitation is cost complexity, because every minute stacks several charges and add-ons on top. Non-technical teams may face a learning curve on complex call flows. Use the $10 free credit to build one simple agent, then measure real per-minute costs before scaling.