Vapi

Vapi is a Web and API platform for developer-led teams building, testing, and deploying voice AI agents that handle inbound and outbound phone calls.

Key capabilities include:

• API-first control with SDKs (Python and TypeScript) to define agent behavior, tool calling, and production integrations.
• Bring-your-own stack support, letting teams choose preferred speech-to-text, LLM, text-to-speech, and telephony providers (including self-hosted models via API keys).
• Voice agent builder and Flow Studio, combining a dashboard for agent setup with no-code conversational design for flows.
• Operational tooling such as automated testing with simulated calls, A/B experiments for prompts, voices, and flows, and call routing using sentiment and contextual triggers.

Pricing: Unknown.

What makes it notable: it targets engineers who need deep configurability and deterministic, guarded call flows rather than a fixed vendor stack, and it is built for low-latency, high-scale voice interactions (including enterprise options such as SOC2, HIPAA, and PCI compliance).