Audio (TTS & transcription)

Two audio endpoints, both OpenAI-shaped:

Text-to-speech (TTS) — POST /v1/audio/speech returns audio bytes for a text input. Find models whose output_modalities includes audio.
Transcription (ASR) — POST /v1/audio/transcriptions returns text for an audio file upload. Find models whose input_modalities includes audio.

See model discovery for the filter snippets — text-to-speech and speech-to-text.

Text-to-speech

The example below uses Kokoro-82M. The response body is raw audio bytes (WAV by default) — write them straight to disk.

curl https://api.flex.ai/v1/audio/speech \
  -H "Authorization: Bearer $FLEXAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "Kokoro-82M",
    "input": "Hello from FlexAI.",
    "voice": "neutral_female"
  }' \
  --output out.wav

import os
from openai import OpenAI

client = OpenAI(base_url="https://api.flex.ai/v1", api_key=os.environ["FLEXAI_API_KEY"])

resp = client.audio.speech.create(
    model="Kokoro-82M",
    input="Hello from FlexAI.",
    voice="neutral_female",
)
resp.stream_to_file("out.wav")

import fs from "node:fs";
import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.flex.ai/v1",
  apiKey: process.env.FLEXAI_API_KEY,
});

const resp = await client.audio.speech.create({
  model: "Kokoro-82M",
  input: "Hello from FlexAI.",
  voice: "neutral_female",
});
fs.writeFileSync("out.wav", Buffer.from(await resp.arrayBuffer()));

Voices

Voice names are model-specific — there’s no shared “Alloy/Echo/Fable/…” namespace. Check the model catalog for the supported set, or fall back to the model’s upstream documentation.

Billing

TTS bills per input character. Read the active rate from GET /v1/pricing — find the row for your model, where pricing_type is per_character, and take unit_price_usd. See also billing.

Transcription

/v1/audio/transcriptions is Whisper-compatible. Send the audio file as multipart/form-data, get back a JSON { "text": "..." }. The current model is whisper-large-v3-turbo.

curl https://api.flex.ai/v1/audio/transcriptions \
  -H "Authorization: Bearer $FLEXAI_API_KEY" \
  -F "file=@input.wav" \
  -F "model=whisper-large-v3-turbo" \
  -F "language=en"

import os
from openai import OpenAI

client = OpenAI(base_url="https://api.flex.ai/v1", api_key=os.environ["FLEXAI_API_KEY"])

with open("input.wav", "rb") as f:
    resp = client.audio.transcriptions.create(
        model="whisper-large-v3-turbo",
        file=f,
        language="en",
    )
print(resp.text)

import fs from "node:fs";
import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.flex.ai/v1",
  apiKey: process.env.FLEXAI_API_KEY,
});

const resp = await client.audio.transcriptions.create({
  model: "whisper-large-v3-turbo",
  file: fs.createReadStream("input.wav"),
  language: "en",
});
console.log(resp.text);

Request fields

Field	Required	Notes
`file`	Yes	`multipart/form-data` upload. WAV, MP3, M4A, FLAC, OGG.
`model`	Yes	Must be a speech-to-text model — on `/v1/models`, `category` is `audio` and `input_modalities` includes `audio`.
`language`	No	ISO-639-1 code (`en`, `fr`, …). Auto-detected when omitted.

Billing

ASR bills per minute of input audio. Read the active rate from GET /v1/pricing — find the row for your model, where pricing_type is per_minute, and take unit_price_usd.

Get Started

Guides

Reference

Chat

Completions

Embeddings

Models

Usage

Audio (TTS & transcription)

Text-to-speech

Voices

Billing

Transcription

Request fields

Billing

See also

​Text-to-speech

​Voices

​Billing

​Transcription

​Request fields

​Billing

​See also

Text-to-speech

Voices

Billing

Transcription

Request fields

Billing

See also