Voice AI infrastructure and orchestration platform for developers
Quick verdict
Vapi is a top choice for developers who want maximum flexibility in choosing STT, LLM, and TTS providers without writing the orchestration layer themselves. It's infrastructure, not a turnkey product, plan for engineering time.
Vapi is one of the most widely used developer platforms for building voice agents from scratch, offering a unified API that stitches together telephony providers, speech-to-text, an LLM of your choice, and text-to-speech into one orchestration layer. It's popular with startups and agencies building custom voice products because it removes the plumbing work of integrating four or five separate vendors while still leaving conversation logic fully in the developer's hands. Vapi also has a large open-source community and marketplace of voice/LLM provider integrations, which keeps it flexible as the underlying model landscape shifts.
Vapi charges based on call minutes and the underlying model/telephony providers used, with a free tier of credits to start.
Developers and agencies building custom voice agent products across multiple use cases.