Skip to main content

Documentation Index

Fetch the complete documentation index at: https://docs.runflow.io/llms.txt

Use this file to discover all available pages before exploring further.

Pricing: $10/1m-tokens. Endpoint: POST /v1/models/google/gemini-tts/runs.
Google’s Gemini TTS converts text to realistic audio. 30 voice presets, multi-speaker synthesis (up to 10 speakers), 24+ languages, and inline style markers for expressive control.

Overview

Pricing

  • Base price: $10/1m-tokens
  • Note: Per 1M tokens (flash, output-dominated)

Gemini TTS API

Endpoint: POST /v1/models/google/gemini-tts/runs

Run the model

Python

import requests

response = requests.post(
    "https://api.runflow.io/v1/models/google/gemini-tts/runs",
    headers={"Authorization": "Bearer RUNFLOW_API_KEY"},
    json={
        "input": {},
        "callback_url": "https://your-server.com/webhook"
    },
)

data = response.json()
print(data)

Node.js

const response = await fetch(
  "https://api.runflow.io/v1/models/google/gemini-tts/runs",
  {
    method: "POST",
    headers: {
      "Authorization": "Bearer RUNFLOW_API_KEY",
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
        "input": {},
        "callback_url": "https://your-server.com/webhook"
    }),
  }
);

const data = await response.json();
console.log(data);

cURL

curl -X POST https://api.runflow.io/v1/models/google/gemini-tts/runs \
  -H "Authorization: Bearer $RUNFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  --data-binary @- <<'JSON'
{
    "input": {},
    "callback_url": "https://your-server.com/webhook"
}
JSON

Request parameters

ParameterTypeRequiredDescription
inputobjectrequiredModel input parameters. See “Input schema” below.
callback_urlstring | nulloptionalWebhook URL - POSTed when the run reaches a terminal state.
metadataobject | nulloptionalArbitrary key-value pairs attached to the run.

Input schema

FieldTypeRequiredAllowed valuesDescription
promptstringrequiredAnyThe text to convert to speech. Gemini TTS supports natural-language prompting for style, pace, accent, and emotional expression - include delivery instructions inline with the text (e.g. ‘Say cheerfully: Have a wonderful day!’). For multi-speaker synthesis, prefix lines with speaker aliases defined in the speakers field (e.g. ‘Alice: Hello!\nBob: Hi!’). Supports inline pace/style markers like [slowly], [whispering], [excited], [extremely fast].
speakersjsonoptionalAnyMulti-speaker voice configuration. When set, enables multi-speaker synthesis where different parts of the text are spoken by different voices. Each speaker needs a voice and a speaker_id (alias) that matches prefixes in the prompt. Requires gemini-2.5-pro-tts or gemini-2.5-flash-tts model. Not supported with gemini-2.5-flash-lite-preview-tts.
output_formatstringoptionalwav, mp3, ogg_opusAudio output format. mp3: compressed, small file size (recommended). wav: uncompressed PCM wrapped in WAV (24 kHz, 16-bit mono). ogg_opus: Ogg container with Opus codec, good quality-to-size ratio.
modelstringoptionalgemini-2.5-flash-tts, gemini-2.5-pro-ttsWhich Gemini TTS model to use. gemini-2.5-flash-tts: low latency, cost-efficient for everyday applications (recommended). gemini-2.5-pro-tts: highest quality, best for structured workflows like podcasts, audiobooks, and customer support.
voicestringoptionalAchernar, Achird, Algenib, Algieba, Alnilam, Aoede, Autonoe, Callirrhoe, Charon, Despina, Enceladus, Erinome, Fenrir, Gacrux, Iapetus, Kore, Laomedeia, Leda, Orus, Pulcherrima, Puck, Rasalgethi, Sadachbia, Sadaltager, Schedar, Sulafat, Umbriel, Vindemiatrix, Zephyr, ZubenelgenubiVoice preset for single-speaker synthesis. 30 distinct voices are available. Ignored when speakers is set. Popular choices: Kore (strong, firm female), Puck (upbeat, lively male), Charon (calm, professional male), Zephyr (bright, clear female), Aoede (warm, melodic female).
language_codestringoptionalAnyLanguage for multilingual synthesis. When set, steers the model to speak in the specified language. Supports 24 GA languages and 60+ Preview languages. If not set, the model auto-detects the language from the text.
temperaturefloatoptionalAnyControls the randomness of the speech output. Higher values produce more creative and varied delivery, while lower values make the output more predictable and focused.
style_instructionsstringoptionalAnyOptional style and delivery instructions prepended to the prompt. Controls expressiveness, accent, pace, tone, and emotional expression using natural language. Use this to separate style control from the text content. Examples: ‘Speak warmly and slowly’, ‘Read this as a dramatic newscast’, ‘Use a British accent with a cheerful tone’, ‘Whisper mysteriously’.

Output schema

FieldTypeDescription
outputsjsonUnified output array - one entry per generated artifact with url/type/width/height/duration/etc.
nsfw_detectedjsontrue if the provider flagged output as NSFW, false if cleared, null if not checked.
seedjsonDeterministic seed used for generation, or null if the provider doesn’t return one.
timingjsonProvider timing info (inference_ms etc.), or null.

Callback payload

When you provide a callback_url, Runflow POSTs to it once the run reaches a terminal state.
FieldTypeDescription
eventstringEvent type: “run.completed”, “run.failed”, or “run.cancelled”.
run_idstringThe unique identifier of the run.
statusstringTerminal status: “succeeded”, “failed”, or “cancelled”.
outputobject | nullThe run output. Null if the run failed or was cancelled.
duration_msnumber | nullTotal run duration in milliseconds.
created_atstring | nullISO 8601 timestamp when the run was created.
completed_atstring | nullISO 8601 timestamp when the run reached terminal state.
metadataobject | nullThe metadata object passed at run creation, if any.
  • Retries: 3 attempts with exponential backoff (1s, 2s). Retries on 5xx / network errors only.
  • Headers: Runflow-Request-Id is always sent. Runflow-Signature is sent if a signing secret is configured.

Additional Resources

Browse all models

Browse the catalog.

Run lifecycle

Callbacks, polling, statuses.

Callbacks

Handle async results.

Pricing

How requests bill out.