Vapi Review — Joute's Take

The Essentials

API platform for AI voice agents with sub-second latency
Pay as you go, around $0.05/minute
STT, LLM, and TTS combined with telephony integrations (Twilio, Vonage)
Built for developers building AI telephony agents who need fine-grained control

What Is Vapi?

Vapi is an API for building AI voice bots with very low latency. It orchestrates the STT (Speech-to-Text) + LLM + TTS (Text-to-Speech) pipeline in a way that minimizes response delay. You pick the LLM (GPT-4, Claude), the voice provider (ElevenLabs, PlayAI, Cartesia), the callable functions, and the telephony integrations. The API is available via REST and webhooks. Vapi has become the go-to for developers building voice agents without wanting to manage the full stack themselves.

Strengths

Sub-Second Latency

Vapi's response latency sits at 500-900ms for natural-feeling conversations. That's the critical threshold for an AI call that doesn't sound robotic.

Total Stack Flexibility

You choose your LLM, your voice, your integrations. Vapi orchestrates without locking you into any technical choices. Want Claude with a Cartesia voice on Twilio? It works.

Well-Documented SDKs

The Python and TypeScript SDKs and Vapi's documentation are among the best in the category. Easy to get started.

Limits

Requires Technical Chops

Vapi is an API, not a no-code builder. For non-developers, Synthflow or Retell are more approachable.

Costs Stack Up in Production

At $0.05/minute, thousands of calls add up fast. Benchmark against alternatives based on your expected volume.

Pricing

Pay as you go, around $0.05/minute of conversation. Check vapi.ai for current rates.

Alternatives

For no-code voice: Synthflow. For another telephony API: Retell AI. For voice agents with enterprise features: Bland AI.

Verdict

Vapi is the API reference for developers building serious voice agents. Latency and flexibility are unmatched. For no-code, Synthflow is more accessible.