MOS | Smallest AI Docs

MOS v2 - higher is better

Metric	Lightning v3.1	Lightning v3.1 Pro	GPT-4o-mini	ElevenLabs Turbo v2.5	ElevenLabs Multilingual v2	Sonic-3	Gemini 2.5 Pro	Gemini 2.5 Flash	MAI-Voice-1	Inworld 1.5	S2 Pro
Mean MOS	NA	4.22	4.16	3.98	4.02	3.76	4.11	4.24	3.97	3.73	3.99
UTMOS	NA	3.76	3.76	3.37	3.41	2.77	3.57	3.71	3.33	2.54	3.50
WV-MOS	4.71	5.05	4.55	4.60	4.63	4.76	4.65	4.76	4.62	4.91	4.48

Mean MOS - Mean Opinion Score: average listener rating on a 1–5 scale across the test set; the canonical aggregate quality metric in TTS evaluation.
UTMOS - A predicted MOS from the UTMOS reference model - an automated proxy for subjective quality.
WV-MOS - A predicted MOS from the WavLM-based WV-MOS reference model - another automated proxy commonly reported alongside UTMOS for cross-validation.

Want to reproduce these results? See the TTS evaluation script to measure TTFB and synthesis quality in your own environment.