Vapi is the developer's choice for building voice agents. You control the composition: pick Anthropic or OpenAI for the brain, ElevenLabs or Deepgram for the voice, and wire in tools and webhooks exactly as you need. The cost is transparency at the expense of latency tuning. You trade lower latency for flexibility and the ability to ship agents in a few hundred lines of code. It is the right pick if you are comfortable owning the full voice stack and your use case doesn't demand sub-second turn-taking.
Retell is the operator's choice for production voice at scale. The platform is tuned for inbound: fast turn-taking, reliable interruption detection, and call analytics built in. You inherit an opinionated stack, but that stack holds up under real call volume and genuinely angry callers. It is the right pick if you are running customer service, appointment scheduling, or other inbound workflows where the quality of the conversation itself is your competitive edge.
For most teams, you pick Vapi if you live in code and own the voice integration, or Retell if you run high-volume inbound and need latency and turn-taking to be someone else's problem. The two platforms coexist: use Retell for your customer-facing inbound agent and Vapi for outbound campaigns or internal voice tooling. If interruption handling and sub-second latency are non-negotiable, Retell. If flexibility and cost transparency matter more, Vapi.