Humanness Index™ · TTS model
by Smallest.ai
Lightning v3.1 is Smallest.ai's flagship text to speech model, a 44.1 kHz engine built for conversational agents with instant voice cloning from a 5 to 15 second sample.
Standings as of Jul 28, 2026, 04:02 UTC
A real arena clip: a cloned source voice reading a customer support prompt at phone quality.
Lightning v3.1 is Smallest.ai's flagship text to speech model, a 44.1 kHz engine built for conversational agents with instant voice cloning from a 5 to 15 second sample. It reads 12 languages with automatic language detection and mid-sentence code-switching, and its launch benchmark published head to head listener wins on EmergentTTS against GPT-4o-mini TTS, ElevenLabs Turbo v2.5 and Multilingual v2, and Cartesia Sonic-3.
Sources: docs.smallest.ai, smallest.ai
The first Smallest.ai entry on the Index, served through the unified Waves API with HTTP, SSE, and WebSocket access. Pay-as-you-go pricing sits at roughly $14.50 per 1M characters, among the lowest rates in the field. In our 50 trial streaming benchmark it returned first audio in a median of 420 ms including network time.
Sources: smallest.ai, docs.smallest.ai
Standings as of Jul 28, 2026, 04:02 UTC
| Rank | Provider | Model | Humanness | Latency |
|---|---|---|---|---|
| #15 | Cartesia | Sonic 2 | 67 | 159 ms |
| #16 | Cartesia | Sonic 3 | 65 | 166 ms |
| #17 | Smallest.ai | Lightning v3.1 | 45 | 420 ms |
| #18 | Neuphonic | neu_hq | 41 | 276 ms |
| #19 | Gradium | Gradium TTS | 35 | 332 ms |
Compare the models in blind tests, read the methodology, or get in touch.
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