AssemblyAI launches its first text-to-speech model, AssemblyAI-TTS-1

AssemblyAI launched AssemblyAI-TTS-1, its first text-to-speech model, built for voice agents. AssemblyAI says it streams in 90 ms at $15 per million characters and calls it the best TTS model you can run at scale on accuracy, naturalness and cost together. OpenRouter says the model is live there, with 4,000+ voices served from the US or EU.

The figures below are Artificial Analysis's own measurements, not AssemblyAI's.

• Provider Voice Arena: Elo 1,227 over 1,626 appearances, ranked #12, just behind Breeze TTS 2 (1,228) and ahead of Mistral's Voxtral 3 TTS (1,221).
• Controlled Voice Arena (same cloned voices): 1,110, ranked #10, behind Cartesia's Sonic 3.5 (1,118); #6 in Knowledge Sharing.
• Pronunciation Robustness: 81.7% across 2,115 rated clips, ranked #16.
• Speed: 162 characters per second, faster than Cartesia's Sonic 3.6 (148.6) and Voxtral 3 TTS (112.3).
• Price: $15 per million characters. Of the eleven models ranked above it on Provider Voice, only two cost less (Gemini 3.8 Flash-Lite TTS at $11 and Simba 3.2 at $6.6); Eleven v4 is $80 and Sonic 3.6 $49.