A practical May 2026 breakdown of the best STT, TTS, and voice agent platforms for production LLM voice systems, with latency, cost, and orchestration trade-offs. Voice agents finally feel like an engineering problem, not a research demo. The pieces are now fast enough to compose into something that feels natural in production. Streaming STT can sit under 300ms, first audio can show up under 100ms, and fast LLMs can stay in the same budget if you pick carefully. What changed for me over the last few weeks was not any single model. It was seeing every layer mature at roughly the same time. This post is my attempt to sort the stack by what actually matters in production, which starts with the shortest possible answer. TL;DR If I had to pick one practical stack right now, I would start with Deepgram Nova-3 plus Flux for STT, Cartesia Sonic Turbo for TTS, GPT-5 mini or Gemini 3.1 Flash for the LLM, and Retell AI for orchestration.…