Top 5 Real-Time Speech-to-Speech APIs and Libraries To Build Voice Agents

Enterprises and developers have two main architectural choices for building conversational voice agents: real-time speech-to-speech (STS) systems, which utilize a large language model (LLM) to process audio input and output, and turn-based systems, which employ a speech-to-text (STT) to LLM to text-to-speech (TTS) pipeline. Real-time STS systems are preferred for their lower latency and simpler architecture, making them suitable for applications requiring live interactions. In contrast, turn-based systems can suffer from high latency and potential information loss, especially in complex languages. Available tools for these architectures include APIs from providers like OpenAI, Gemini, Amazon, and Azure, each offering specific features such as voice activity detection and seamless integration with various connection protocols like WebRTC and WebSockets. Real-time voice AI is still developing, but its potential for low-latency, multimodal interactions suggests it could become a standard in future applications.