Both AssemblyAI and Deepgram now offer dedicated voice agent APIs. Both use a cascaded architecture—separate STT, LLM, and TTS models working in sequence rather than a single multimodal model. Both charge around $4.50/hr. On the surface, they look pretty similar. But when you dig into the details that actually matter for production voice agents—speech accuracy on real-world entities, developer experience, and mid-conversation flexibility—meaningful differences emerge. Here's an honest comparison. Feature AssemblyAI Voice Agent API Deepgram Voice Agent API Pricing $4.50/hr flat ~$4.50/hr + concurrency metering ASR model Universal-3 Pro Streaming (#1 WER) Nova-3 Word accuracy 94.07% (6.3% mean WER) 92.10% Missed entity rate (emails, phones, names) 16.7% 25.5% End-to-end latency ~1 second ~1–1.5 seconds Languages EN, ES, FR, DE, IT, PT EN, ES, NL, FR, DE, IT, JA Turn detection Speech-aware VAD (semantic + neural) Traditional VAD Mid-session updates Prompt + voice + tools + VAD Prompt + voice only Session…