Retell AI

Retell AI is infrastructure for voice agents that need to live inside your product, not on a separate phone line. The core pitch is latency under 800ms and a web SDK that handles the messy bits of real-time audio streaming. I've used it to build a voice intake flow for a legal clinic, and the autonomy here is narrower than you might expect: Retell handles turn-taking, interruption detection, and voice synthesis, but you still define the conversation flow and hook in your own logic for anything beyond simple Q&A. What it does well: embedding voice into existing web or mobile apps without wrestling with WebRTC plumbing. The SDK gives you callbacks for transcript events, so you can trigger actions mid-conversation (updating a form, fetching data, branching logic). The latency is genuinely good, better than stitching together Whisper and ElevenLabs yourself. Multilingual support is solid, and the voice quality is polished enough for customer-facing apps. Where it stumbles: you're paying for infrastructure, not intelligence. Retell doesn't plan or iterate on its own; it executes the conversation graph you define. If you need an agent that autonomously decides when to escalate to a human or dynamically adjusts its strategy, you'll need to build that logic yourself. The pricing is also opaque until you talk to sales, which is frustrating for smaller teams trying to budget. Compared to Bland AI or Vapi, Retell skews more developer-focused. Bland is faster to prototype with but harder to customise; Vapi sits somewhere in between. I'd reach for Retell when I need tight control over the conversation flow and I'm embedding voice into an app where latency matters. For simple outbound calling or internal tools, the setup overhead isn't worth it. One concrete workflow: a voice-driven onboarding form for a healthcare app. The agent asks intake questions, validates answers in real time (checking insurance eligibility via API mid-conversation), and writes structured data to the backend. Retell handled the voice layer; I handled the business logic. That division of labour worked, but don't mistake it for full autonomy.