Cartesia Sonic 3 / 3.5
Cartesia Sonic 3 / 3.5 is a state-space-model text-to-speech (TTS) system with a time-to-first-audio of roughly 40–90ms, with Sonic 3.5 generally available in May 2026. It powers the Line voice-agent platform, which defaults to Sonic 3.5 for TTS and Ink-2 for speech-to-text as of May 2026.