They're definitely anime-style voices, though most of the female ones are very annoying. I couldn't stand to watch an anime with them.

They just sound like anime voices

The voice actors usually try to match the timing of the mouth flaps in the animation. It's hard to do that while also conveying the meaning of what is said correctly (enough) -- and practically impossible to do that while sounding natural in English too.

Prosody is hard. No AI voice I've heard really nails voice generation with fully smooth and human-like cadence and quality, but they're gradually getting better. Airy voices sound a bit tinny and childish, but even so, they're better than many I've heard, including for the elusive "humanness" quality.

Thanks! Airy runs on a proprietary TTS model that we built in-house, rather than a third-party model.