Gemini 3.1 Flash TTS (Preview) API — pricing & specs

Gemini 3.1 Flash TTS (Preview) is a text-to-speech model from Google DeepMind. On KeepRouter, Gemini 3.1 Flash TTS (Preview) costs $1.00 per 1M input tokens and $0.000500 per second of audio, billed pay-as-you-go with no monthly fee. Call it through a compatible KeepRouter endpoint supported by its active route, with the model id gemini-3.1-flash-tts-preview.

MakerGoogle DeepMind
ModalityText-to-speech
Input price$1.00 per 1M tokens
Output price$0.000500 per second of audio
CapabilitiesText-to-speech
EndpointPOST /v1/audio/speech
Model idgemini-3.1-flash-tts-preview

How pricing works for Gemini 3.1 Flash TTS (Preview)

Gemini 3.1 Flash TTS (Preview) is billed for input tokens and per second of generated audio — $1.00 per 1M input tokens and $0.000500 per second of audio. There is no monthly fee; the charge follows measured input tokens and the length of the audio the model returns.

Calling Gemini 3.1 Flash TTS (Preview) on KeepRouter

Point a compatible client at the supported KeepRouter endpoint and set the model to gemini-3.1-flash-tts-preview. KeepRouter preserves the client-facing request shape while handling upstream routing or translation. Send text-to-speech requests to POST /v1/audio/speech.

cURL

curl https://keeprouter.com/v1/audio/speech \
  -H "Authorization: Bearer $KEEPROUTER_KEY" -H "Content-Type: application/json" \
  -d '{"model":"gemini-3.1-flash-tts-preview","input":"Hello from KeepRouter","voice":"alloy"}' --output speech.mp3

Python

import os
from openai import OpenAI
client = OpenAI(base_url="https://keeprouter.com/v1", api_key=os.environ["KEEPROUTER_KEY"])
audio = client.audio.speech.create(model="gemini-3.1-flash-tts-preview", input="Hello from KeepRouter", voice="alloy")

JavaScript

const res = await fetch("https://keeprouter.com/v1/audio/speech", {
  method: "POST",
  headers: { Authorization: "Bearer " + process.env.KEEPROUTER_KEY, "Content-Type": "application/json" },
  body: JSON.stringify({ model: "gemini-3.1-flash-tts-preview", input: "Hello from KeepRouter", voice: "alloy" }),
});

Estimate API costs

At the current KeepRouter customer price, an example workload of 1,000 input tokens and 6 seconds of generated audio per request costs approximately $0.004000 per request. At 100 requests per day, that is $12.00 over 30 days. This is a usage estimate, excluding processing fees, taxes, retries and application infrastructure. Actual usage, cache hits and supported generation durations need their own checks.

Adjust quantities in the API cost calculator.

How to evaluate Gemini 3.1 Flash TTS (Preview)

Gemini 3.1 Flash TTS (Preview) is listed on KeepRouter as text-to-speech under the exact id gemini-3.1-flash-tts-preview. Use /v1/audio/speech for the listed route; a maker's upstream features do not automatically apply to this gateway endpoint. No context limit is asserted here because the exact upstream limit has not been verified for this catalog entry.

First workload: Synthesize a representative script and measure returned audio duration, intelligibility, startup delay and cost per generated second.

Before production: Output billing is duration-based; do not interpret the published output rate as a per-million-token price.

Public model usage evidence

No public, exact-variant usage figure has been verified for this KeepRouter model id. Missing data is not zero usage; family-level or maker-wide traffic is not presented as this model's traffic.

Published examples and cases

No exact-model customer case has been verified for this entry. The workload above is an evaluation recipe, not a claim of a public deployment.

Source and verification boundary

Official Google DeepMind website. KeepRouter's live catalog is authoritative for the customer price and enabled endpoint shown here; the maker remains authoritative for upstream model capabilities and limits.

Pricing and implementation guides

Related models

All models & pricing · Quickstart · KeepRouter vs OpenRouter · Glossary · Get an API key

Catalog facts and prices last changed .

Page content reviewed .