OpenAI Realtime API vs Vapi

Pick two tools from the same category to compare side-by-side.

	OpenAI Realtime API Speech-to-speech realtime model API for building low-latency voice agents.	Vapi Voice AI platform: STT, TTS, telephony, turn-taking for voice agents.
Category	voice	voice
Vendor type	commercial	commercial
Pricing	usage	usage
Strengths	+ Single model handling speech-to-speech with reasoning and tool calling + Multiple transports including WebRTC, WebSocket, and SIP for telephony + Low-latency persistent sessions for natural turn-taking + Specialized variants for live translation and streaming transcription	+ End-to-end voice stack in one product + Mature telephony integration + Turn-taking primitives
Tradeoffs	− Locked to OpenAI models with no provider choice − Closed, cloud-only API − Realtime audio pricing can be costly at scale	− Less control than assembling individual layers
Used in stacks	0	1