New Sign up free, 10 calls on us. Up to $1, no card needed.

TTS-1 HD

TTS-1 HD is OpenAI's text-to-speech model optimized for quality, the higher-fidelity half of the pair it forms with tts-1.

Input
text $30/M
Output
audio
Context
4K

Price in context

Where the price sits among 7 comparable models

Input$30/M
$4 · Google TTS Standard Google TTS Chirp 3 HD · $30

The bar shows how this model’s price compares with every other model of the same kind on Synthorai. The cheapest and the most expensive are named at each end. These are base rates; batch, region and cache-write discounts are on the pricing page.

Specs & limits

Text to speech

Synthesis languages Generally follows the Whisper model’s language support: Afrikaans, Arabic, Armenian, Azerbaijani, Belarusian, Bosnian, Bulgarian, Catalan, Chinese, Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, Galician, German, Greek, Hebrew, Hindi, Hungarian, Icelandic, Indonesian, Italian, Japanese, Kannada, Kazakh, Korean, Latvian, Lithuanian, Macedonian, Malay, Marathi, Maori, Nepali, Norwegian, Persian, Polish, Portuguese, Romanian, Russian, Serbian, Slovak, Slovenian, Spanish, Swahili, Swedish, Tagalog, Tamil, Thai, Turkish, Ukrainian, Urdu, Vietnamese and Welsh, despite voices being optimized for English
Voices alloy, ash, coral, echo, fable, onyx, nova, sage and shimmer, a smaller set than the full 13-voice TTS list, and voices are currently optimized for English.
Input limit 4,096 characters Vendors publish this cap in different units: a byte cap is not a character cap for non-Latin text.
Streaming synthesis Yes
SSML Not documented
Voice control None on this model
Billing unit Per character of input
Endpoints and formats
  • Speech generation endpoint (v1/audio/speech) only, with Chat Completions, Responses, Realtime, Batch and Fine-tuning all listed as not supported
  • input text is capped at 4096 characters
  • output mp3 (default), opus, aac, flac, wav or pcm (raw 24 kHz 16-bit signed little-endian samples)
  • realtime playback via chunked transfer encoding

Model

Modalities text → audio

Text-to-speech model optimized for quality: the same Speech endpoint as tts-1, tuned for high-quality rather than low-latency use cases. The instructions parameter that steers accent, emotion, intonation and tone on gpt-4o-mini-tts does not work with tts-1 or tts-1-hd.

per OpenAI official docs ↗

Use TTS-1 HD in 30 seconds

OpenAI-compatible: swap the base_url, keep your SDK. POST /v1/chat/completions

from openai import OpenAI

client = OpenAI(
    base_url="https://synthorai.io/v1",
    api_key="sk-syn-...",
)

resp = client.chat.completions.create(
    model="tts-1-hd",
    messages=[{"role": "user", "content": "Summarize this diff"}],
)
print(resp.choices[0].message.content)

About TTS-1 HD

  • The model page frames it as converting text to natural sounding spoken text for high quality text-to-speech use cases, and the guide states the trade directly: tts-1 provides lower latency, but at a lower quality than tts-1-hd.
  • That extra quality is the whole difference, and it is priced accordingly at $30 per million characters, double the tts-1 rate, which makes it the choice for narration, published audio, and anything a listener will hear more than once rather than for interactive turn-by-turn speech.
  • Everything else is shared with its sibling.
  • It serves only the Audio API speech endpoint, taking text in and returning audio, with the same nine voices (alloy, ash, coral, echo, fable, onyx, nova, sage, and shimmer), the same MP3, Opus, AAC, FLAC, WAV, and 24 kHz PCM output formats, the same 0.25 to 4.0 speed range around a default of 1.0, and the same chunked-transfer streaming so playback can start early.
  • The same two restrictions apply as well: the instructions parameter for steering tone and delivery is documented as not working on tts-1 or tts-1-hd, and the sse stream format is unsupported, leaving raw audio streaming as the only option.
  • Language coverage follows Whisper's list while the voices stay optimized for English, and OpenAI requires a clear disclosure that the voice is AI-generated.
  • Synthorai serves TTS-1 HD through the same OpenAI-compatible /v1/audio/speech endpoint.

FAQ

Is the TTS-1 HD API free to try?

Yes: new accounts get 10 trial calls and up to $1 in free credit, no card required. That's enough to try TTS-1 HD against your real workload before adding a payment method.

What is TTS-1 HD best at?

Optimized for quality rather than latency; double the tts-1 rate at $30 per million characters; suits narration and published audio, not interactive speech. See the About section for the full picture from the vendor's own release notes.

How much does TTS-1 HD cost?

TTS-1 HD costs $30 per million input tokens and $0 per million output tokens on Synthorai. That is the provider's list price, with no platform markup.

Does TTS-1 HD support prompt caching?

TTS-1 HD has no cache-read discount on Synthorai today. Prompt caching still applies to other models on the gateway; see the pricing table for cache-enabled alternatives. Provider caching comparison →

How do I get access to TTS-1 HD?

Point your existing OpenAI SDK at base_url="https://synthorai.io/v1", set model="tts-1-hd", and you're done. One API key covers every model on the gateway.

Related models

Compare

Every value on this page is transcribed from the vendor's own documentation, linked above, and carries the date it was checked. Prices are compared across the catalogue; specification values that vendors define differently are shown with the difference stated rather than charted. Nothing here is measured by us, and nothing is scored.

Get your API key Compare your cost →