Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS at a glance

Gemini 3.8 Flash TTS and Gemini 3.1 Flash TTS are both Google models in the Audio Generation category, available through the EmpirioLabs API.

Key differences

• Gemini 3.8 Flash TTS is the newer release (Sep 22, 2026); Gemini 3.1 Flash TTS was released on Apr 13, 2026.
• Capabilities listed only for Gemini 3.8 Flash TTS: voice tags, voice control, streaming, voice cloning.
• Gemini 3.8 Flash TTS lists the lower rate for Output (per 1M generated tokens).
• Both models list the same rate for Input (per 1M prompt tokens).

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS: specs

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS: API pricing

Live rates from the EmpirioLabs catalog for both models. Each rate card always matches what the API charges.

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS: API parameters

Request parameters each model lists on EmpirioLabs, with the allowed values or range where one applies. A dash marks a parameter the model does not list.

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS: limits and notes

Gemini 3.8 Flash TTS

Limits

• Text: up to 5,000 characters per request
• Audio billing: 32 output tokens per second of generated audio
• 130 languages. The language of the text is detected automatically.

Voices

• The 30 voices in the voice list speak every supported language.
• GET /v1/voices?model=gemini-3-8-flash-tts lists the full library of more than 2,000 voices across 30 locales, with the language, accent, gender, pitch, and a description of each. Filter it with language, gender, pitch, or q. Any id it returns works as voice or voice2; when you also set language, use the voice's own language.

Custom voices

• Set voice to custom and pass two recordings of the same adult speaker as https URLs: voice_audio_url, 10 to 30 seconds of natural speech, and voice_consent_audio_url, the speaker reading "I am the owner of this voice and I consent to Google using this voice to create a synthetic voice model." The statement is accepted in 30 languages; consent_statements on that parameter lists each wording.
• Both must be recordings of a real person, in a quiet room on the same microphone. AI-generated audio is not accepted. WAV, MP3, M4A, OGG, WEBM and FLAC are accepted, up to 15 MB each.
• The response includes voice_id and voice_id_expires_at. Pass the voice_id as voice or voice2 to reuse the voice for 7 days without new recordings. A voice_id works only for the account that created it.
• This model keeps no list of custom voices, so keep the voice_id from the response. A custom voice ends when its id expires, so there is nothing to delete.
• In the Playground, set Voice to Custom to use a voice made in the same tab again, or copy its id.

Delivery direction

• Put direction for the whole passage in style_prompt rather than in the text, for example "warm, unhurried, and reassuring".
• Place vocal tags inline where the sound should happen. Use these English tags even when the text is in another language:

<argh> <breath> <heavy breath> <exhales> <cackle> <cheer> <chuckle> <chuckles> <cough> <cry> <gasp> <giggle> <groan> <growl> <grunt> <grr> <hiss> <laugh> <laughter> <moan> <pant> <pff> <phew> <scream> <shout> <shriek> <sigh> <sighs> <sneeze> <snicker> <snort> <sob> <throat-clearing> <tsk> <whimper> <whispers> <whispering> <yawn> <short pause> <long pause>

• Capitalize a word to stress it. Wrap a listener reaction in pipes, for example |mm-hmm|, to add it without starting a new turn.

Multi-speaker

• Up to two speakers per request. Start each line with a speaker name and a colon, for example Speaker1: and Speaker2:. The names must match speaker1_name and speaker2_name.

Output

• WAV, MP3, OGG (Opus), ALAW, or MULAW, at 8,000 to 48,000 Hz.
• POST /v1/audio/speech:stream sends 16-bit PCM chunks at 24,000 Hz while the audio is generated, then the complete file in the requested format. speed is available on POST /v1/audio/speech only.

Gemini 3.1 Flash TTS

Most controllable Gemini TTS to date.

Limits

• Text + style prompt: 4,000 bytes each (8,000 combined)
• Max output: ~10 minutes
• Audio billing: ~25 tokens per second (~15 chars/s)
• Language is auto-detected; the language setting is a hint, not a constraint

Inline audio tags (control delivery)

• Emotion: [whispers], [shouts], [laughs], [sighs], [cheerful], [sad], [angry], etc.
• Pace: [slow], [fast], [extremely fast], [normal pace]
• Pauses: [short pause], [long pause], [breath]
• Emphasis: [softly], [loudly], [high pitch], [low pitch], [rising tone], [falling tone]

How to call Gemini 3.8 Flash TTS and Gemini 3.1 Flash TTS

Gemini 3.8 Flash TTS serves speech through POST /v1/audio/speech and returns playable audio. Send the text to speak as input with the model id gemini-3-8-flash-tts. Both models are called through the same endpoint. Set model to gemini-3-8-flash-tts or gemini-3-1-flash-tts. Get an API key from the EmpirioLabs dashboard.

curl https://api.empiriolabs.ai/v1/audio/speech \
  -H "Authorization: Bearer $EMPIRIOLABS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemini-3-8-flash-tts",
    "input": "Welcome to EmpirioLabs. Your build just finished."
  }' \
  --output speech.mp3

Gemini 3.8 Flash TTS vs Gemini 3.1 Flash TTS: common questions

What is the difference between Gemini 3.8 Flash TTS and Gemini 3.1 Flash TTS?

Gemini 3.8 Flash TTS is the newer release (Sep 22, 2026); Gemini 3.1 Flash TTS was released on Apr 13, 2026. Capabilities listed only for Gemini 3.8 Flash TTS: voice tags, voice control, streaming, voice cloning. Gemini 3.8 Flash TTS lists the lower rate for Output (per 1M generated tokens). The specs, rate cards, and parameters on this page come from the live EmpirioLabs catalog.

Which is newer, Gemini 3.8 Flash TTS or Gemini 3.1 Flash TTS?

Gemini 3.8 Flash TTS is the newer release (Sep 22, 2026); Gemini 3.1 Flash TTS was released on Apr 13, 2026.

Which has the lower rate, Gemini 3.8 Flash TTS or Gemini 3.1 Flash TTS?

Gemini 3.8 Flash TTS lists the lower rate for Output (per 1M generated tokens). Both models list the same rate for Input (per 1M prompt tokens). Both live rate cards are on this page and always match what the API charges.

Can I switch between Gemini 3.8 Flash TTS and Gemini 3.1 Flash TTS without rebuilding my integration?

Yes. Both models use POST /v1/audio/speech with the same EmpirioLabs API key, so most integrations switch by changing the model value. Check the parameters table on this page first if you rely on a model-specific parameter.

Can I try Gemini 3.8 Flash TTS and Gemini 3.1 Flash TTS in the browser before integrating?

Yes. Open each model in the EmpirioLabs playground and run the same prompt on both, with the parameters the API exposes.