/openrouter-tts

name: openrouter-tts
description: Generate speech audio from text using OpenRouter's text-to-speech API. Use when the user asks to synthesize speech, narrate text, create a voiceover, generate an audiobook clip, read text aloud, convert text to an audio file, or mentions TTS, text-to-speech, or voice synthesis.

OpenRouter Text-to-Speech

Synthesize speech via `POST /api/v1/audio/speech` using `curl`. The endpoint is OpenAI-compatible, so the OpenAI SDKs work by pointing them at `https://openrouter.ai/api/v1`. Requires `OPENROUTER_API_KEY` (get one at https://openrouter.ai/keys). If unset, stop and ask.

One call, raw bytes back

The response body is the audio bytes — write them to a file with the extension matching `response_format`. It is **not JSON**; error responses are, so only try to parse JSON when the status is non-200.

Two response headers are worth keeping:

• `Content-Type` — `audio/mpeg` for mp3; for pcm it includes the sample rate and channel count, e.g. `audio/pcm;rate=24000;channels=1`. Parse these parameters if you need to wrap the raw bytes into a WAV container.
• `X-Generation-Id` — the generation ID (format `gen-tts-<timestamp>-<suffix>`), useful for tracking, debugging, and cost lookups.

Drop-in workflow

#!/usr/bin/env bash
set -euo pipefail

MODEL="openai/gpt-4o-mini-tts-2025-12-15"
VOICE="alloy"
FORMAT="mp3"                          # mp3 or pcm
INPUT="Hello! This is a text-to-speech test."
OUTPUT="speech-$(date +%Y%m%d-%H%M%S).${FORMAT}"
HEADERS=$(mktemp)

payload=$(jq -n --arg model "$MODEL" --arg input "$INPUT" \
               --arg voice "$VOICE" --arg fmt "$FORMAT" \
  '{model: $model, input: $input, voice: $voice, response_format: $fmt}')

http_code=$(curl -sS -X POST https://openrouter.ai/api/v1/audio/speech \
  -H "Authorization: Bearer $OPENROUTER_API_KEY" \
  -H "Content-Type: application/json" \
  -D "$HEADERS" \
  --output "$OUTPUT" \
  -w '%{http_code}' \
  -d "$payload")

if [[ "$http_code" != "200" ]]; then
  echo "TTS failed (HTTP $http_code):" >&2
  cat "$OUTPUT" >&2                   # error body is JSON, not audio
  rm -f "$OUTPUT" "$HEADERS"
  exit 1
fi

gen_id=$(grep -i '^x-generation-id:' "$HEADERS" | awk '{print $2}' | tr -d '\r')
rm -f "$HEADERS"
echo "Saved $(realpath "$OUTPUT") (generation_id=${gen_id:-unknown})"

Discovering TTS models and voices

Filter the models endpoint by output modality to list speech models. Each model carries a `supported_voices` array with the exact voice IDs that provider accepts.

# Models + voices in one shot
curl -sS "https://openrouter.ai/api/v1/models?output_modalities=speech" \
  | jq '.data[] | {id, name, supported_voices, pricing}'

# Just the voices for a specific model
curl -sS "https://openrouter.ai/api/v1/models?output_modalities=speech" \
  | jq -r '.data[] | select(.id=="openai/gpt-4o-mini-tts-2025-12-15") | .supported_voices[]'

Voices are provider-namespaced: OpenAI uses short names (`alloy`, `nova`), Voxtral encodes language + persona + emotion (`en_paul_happy`), Kokoro prefixes with language/gender (`af_bella` = American female Bella).

Parameters

| Field | Required | Notes | | ----------------- | -------- | ----------------------------------------------------------------------------------------------------------------- | | `model` | yes | TTS model slug (e.g. `openai/gpt-4o-mini-tts-2025-12-15`, `mistralai/voxtral-mini-tts-2603`). | | `input` | yes | The text to synthesize. | | `voice` | yes | Voice identifier. Look up the exact set for your model in `supported_voices` on the models endpoint (see the discovery section above). Voices are provider-namespaced — e.g. `alloy` is an OpenAI voice and will not work on Voxtral or Kokoro. | | `response_format` | no | `mp3` or `pcm`. Default is `pcm`. **Set this explicitly** — the default is usually not what a user wants to save. | | `speed` | no | Playback multiplier (e.g. `1.25`). Honored by OpenAI TTS. Other providers may accept and ignore it, or reject unknown fields — check the provider's behavior if it matters. | | `provider` | no | Provider passthrough — see below. |

Picking a format

• **`mp3`** (`audio/mpeg`) — compressed, ready to play in any audio app. Default choice for files the user will listen to or share.
• **`pcm`** (`audio/pcm;rate=<rate>;channels=<n>`) — uncompressed raw samples. The response `Content-Type` carries the sample rate and channel count (e.g. `rate=24000;channels=1` for OpenAI TTS), which you'll need if you wrap the bytes into a WAV container. Lower latency for real-time streaming pipelines, but not directly playable on its own. Pick this only when the user explicitly wants raw audio or is piping into a streaming system.

Match the file extension to the format — saving pcm bytes as `.mp3` produces a file no player will open, and this is the most common cause of "empty/corrupted audio" reports.

Provider-specific options

Provider passthrough goes under `provider.options.<slug>` and is only forwarded when that provider handles the request. The most useful one is OpenAI's `instructions`, which steers tone, accent, pacing, or emotion without retraining:

{
  "model": "openai/gpt-4o-mini-tts-2025-12-15",
  "input": "Welcome to the show.",
  "voice": "alloy",
  "response_format": "mp3",
  "provider": {
    "options": {
      "openai": {
        "instructions": "Speak in a warm, friendly tone with a slow pace."
      }
    }
  }
}

For other providers, check each provider's upstream docs for available passthrough keys — naming conventions vary (camelCase for OpenAI/Google, snake