Gemini 3.8 Flash TTS: turning director-level voice direction into API parameters
Google's speech generation model (gemini-3.8-flash-tts), positioned for studio-grade voice fidelity, expressive acting and long-form stability, the most overlooked being the last: audiobook failure is not an ugly sentence but timbre drift by hour three. The design separates scopes: text is strictly a script while performance direction travels on another channel and is never read aloud, fixing "(sighs)" that used to be spoken; round style goes into speech_metadata.style, word-level emotion into pipe tags. Four voice sources: prebuilt, an extended library, voice design IDs (describe it, then reuse) and replication IDs; design and replication arrived only in 3.8. Specs: 130 languages with automatic language detection, WAV by default at 24 kHz, at most 2 speakers per request and only with prebuilt voices. Billing is per audio token at 25 tokens per second, $0.50 input and $9.00 output per million through 2026-12-31 then $1.00/$18.00. Limits: 24 kHz is not mastering grade; replication compliance rests with the user. No speech board among the 12 we sync, so listed alongside ElevenLabs v3 without ranking. Graded C (vendor-stated): no intelligibility or blind listening test by us.