Retell AI

Retell AI is a conversational voice AI platform purpose-built for businesses that want to automate inbound and outbound phone calls with AI agents that sound and respond like real humans. Backed by Y Combinator and rated 4.8 on G2 with hundreds of customer reviews, the platform lets product, support, and operations teams design, deploy, and scale phone agents that handle appointment booking, lead qualification, customer support, debt collection, surveys, and IVR replacement without requiring a deep speech engineering background.

The core technology stack focuses on the three problems that have historically made voice agents feel robotic: latency, turn-taking, and naturalness. Retell AI orchestrates speech-to-text, large language models, and text-to-speech with response latencies low enough to support real-time back-and-forth dialogue, and its turn-taking model is tuned to detect when a caller has finished speaking, when they are pausing mid-thought, and when they are interrupting the agent. The result is a conversation that flows closer to a human call than the rigid prompt-response cadence of traditional IVR or earlier voice bots.

Developers can build agents three ways: a single-prompt agent driven entirely by an LLM system prompt, a conversation-flow builder for multi-step deterministic logic with branching and tool calls, or a custom LLM endpoint where teams plug in their own model and reasoning stack while Retell handles the voice, telephony, and turn-taking layer. Agents can call functions, look up data in external systems, transfer calls to human representatives, send post-call SMS, and trigger webhooks for downstream workflows. Built-in telephony lets users buy phone numbers directly inside the dashboard, and SIP trunking is supported for organizations that need to bring their own carrier or integrate with existing contact-center infrastructure.

Retell AI also ships an extensive voice library spanning multiple languages and accents, plus support for voice cloning so businesses can match a brand persona. Operations teams get batch-call dispatch for outbound campaigns, a dialer for high-volume calling, real-time and post-call analytics, transcripts, recordings, sentiment scoring, and concurrency that scales into the thousands of simultaneous calls. The platform exposes a REST API and SDKs, integrates with CRMs and scheduling tools through Zapier, n8n, and webhooks, and offers HIPAA-compliant deployments for healthcare workflows along with SOC 2 controls for regulated industries. Pricing is fully usage-based at a per-minute rate, with separate charges for telephony, voice synthesis, and LLM inference, which keeps cost predictable per call but requires careful modeling for high-volume use cases.