Google Launches Gemini 3.1 Flash TTS

Google released Gemini 3.1 Flash TTS, a new text-to-speech model available in public preview on Google AI Studio and Vertex AI. The model emphasizes precise controllability and expressivity across 70+ languages and supports 200+ audio tags for steering style, pacing, accent, and delivery. Generated audio is embedded with the SynthID watermark to help identify AI-origin content.

Gemini 3.1 Flash TTS accepts natural-language prompts plus inline audio tags enclosed in square brackets to modulate delivery. The documented prompting formula is: [pacing tag] + spoken text + [expressive tag] + spoken text + [pause tag] + spoken text. Developers select a baseline voice then layer stylistic instructions or audio tags to change accent, tone, pacing, and emotional cues. Key capabilities highlighted:

• •Fine-grained stylistic control via 200+ audio tags for pacing, emphasis, and expressivity
• •Multilingual output across 70+ languages and region-specific accent guiding
• •Integrated provenance using SynthID watermarking in audio outputs

This release shifts the TTS usability bar from simple neural voice generation toward production-ready, controllable speech. The inline tag approach mirrors prompt-engineering patterns in LLMs, making it easier for practitioners to iterate on voice UX without low-level signal manipulation. Watermarking with SynthID addresses provenance and moderation needs increasingly important for regulated industries and content platforms. Compared with prior cloud TTS offerings, the emphasis here is on expressivity and direct prompt control rather than only voice cloning or concatenative techniques.

Adoption will hinge on tooling around tag libraries, latency and cost on Vertex AI, and real-world robustness across long-form narration and mixed-content streams. Monitor documentation updates for tag semantics, SDK samples, and any fine-tuning or customization options that extend beyond prompt-based control.