Developer audio and voice-agent SDKs cover the building blocks for conversational applications that combine speech-to-text, large language models, and text-to-speech. As of 2026-05-18, this space is defined by a mix of general-purpose cloud audio APIs and specialized stacks tuned for real-time interaction, voice cloning, and vertical phone agents. OpenAI’s audio models and SDKs provide an integrated path to pair robust speech transcription and audio generation with LLM capabilities. Competing offerings emphasize different trade-offs: ElevenLabs delivers production-grade expressive TTS, high-fidelity voice cloning, and transcription; Voila provides open-source, low-latency full‑duplex voice-language models for persona-aware, real-time role-play; ZenCall.ai and Vocea target phone-agent workflows for call answering, routing, and appointment management; AudioBrief and Speak Pen focus on lightweight TTS/STT for content summarization and note capture; Tate-A-Tate and similar no-code platforms lower the barrier to orchestration and deployment of voice agents. Current trends include convergence of LLMs with speech pipelines, demand for sub-second round-trip latency in conversational agents, rising interest in controllable voice cloning, and more attention to privacy and deployment options (cloud vs on-prem or edge). For developers choosing an SDK, key considerations are latency and duplex support, voice quality and cloning fidelity, ease of orchestration with LLMs, vertical feature sets (telephony integrations, calendaring), pricing, and open-source vs proprietary licensing. This comparison helps developers weigh integrated platforms like OpenAI against specialized SDKs when building scalable, production-ready voice agents and multimodal conversational products.