The API

Host: every request goes to https://tts.thinnest.ai.
Key: use a full-access API key from Settings → API keys, sent as Authorization: Bearer <key>. A build or read-only key cannot speak, because speech spends money.
A developer acting for a customer: add X-Workspace: <customer id>, as on the rest of the API.

OpenAI-compatible: `POST /v1/audio/speech`

This takes the same request as OpenAI’s speech API, so OpenAI SDKs and the tools built on them work with two changes: the base URL https://tts.thinnest.ai/v1 and your key.

curl https://tts.thinnest.ai/v1/audio/speech \
  -H "Authorization: Bearer $THINNEST_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"model": "aero-tts", "voice": "anvi", "input": "नमस्ते! आपका ऑर्डर कल पहुँच जाएगा।", "response_format": "mp3"}' \
  --output speech.mp3

Field	Values
`model`	`aero-tts` (`tts-1` and `gpt-4o-mini-tts` are accepted as the same)
`voice`	A voice id, such as `anvi` or `arjun`, or one of your cloned voices. OpenAI’s names (`alloy`, `nova`, `echo`, `onyx` and the rest) are accepted and speak as Anvi or Arjun
`input`	Up to 4,000 characters
`response_format`	`mp3` (default), `opus`, `wav`, `pcm` (24 kHz, 16-bit, mono)
`speed`	`1.0` only, for now
`language`	Optional, not in OpenAI’s schema: a code such as `hi`. Leave it out and the script decides

Native: `POST /v1/speech`

This adds what OpenAI’s shape cannot carry: 8 and 16 kHz output, and mu-law for phone lines.

{ "text": "...", "voice": "anvi", "language": "auto", "format": "mulaw", "sample_rate": 8000 }

format: pcm, wav, mulaw, mp3 or opus.
sample_rate: 8000, 16000 or 24000. mp3 and opus are 24000 only.
Streaming: audio streams back as it is made.
Headers: the response carries X-Request-Id, X-Characters (what the request counted, free or charged), and X-Concurrency-Limit and X-Concurrency-In-Use.

WebSocket: `wss://tts.thinnest.ai/v1/stream`

One connection carries many utterances, each with an id, and each can be cancelled mid-sentence. Use it for live conversations.

You send	We send
`{"type":"speak","id":"u1","text":"...","voice":"anvi","format":"pcm","sample_rate":24000}`	`{"type":"audio","id":"u1","audio":"<base64>"}` for each chunk
`{"type":"cancel","id":"u1"}`	then exactly one `{"type":"end","id":"u1","chars":42}` or `{"type":"error",...}`
`{"type":"ping"}`	`{"type":"pong"}`

To get raw bytes instead of base64, add "binary": true. Each frame is then: 1 byte for the id’s length, the id, then the audio. Browsers cannot send an Authorization header on a WebSocket, so connect from your server.

Voices

GET https://app.thinnest.ai/api/v1/tts/voices lists the catalogue.

Errors

Status	Code	What to do
400	`validation_failed`	Fix the field the message names
401	`unauthorized`	Check the key
402	`insufficient_balance`	Your free characters and wallet are used up. Add money to your wallet
403	`not_available`	Aero TTS is not on for this workspace, for example one billed in another currency
429	`concurrency_limit`	Your plan’s requests-at-once limit: retry after one finishes
429	`rate_limited`	Over 600 requests a minute: slow down
503	`overloaded`	Briefly busy: retry after `Retry-After`

Getting started

Text-to-Speech

Your agent

Channels

Put it on your site

Reaching out

Meta's rules

Working the conversations

White label

Partners

OpenAI-compatible: `POST /v1/audio/speech`

Native: `POST /v1/speech`

WebSocket: `wss://tts.thinnest.ai/v1/stream`

Voices

Errors

​OpenAI-compatible: POST /v1/audio/speech

​Native: POST /v1/speech

​WebSocket: wss://tts.thinnest.ai/v1/stream

​Voices

​Errors

OpenAI-compatible: `POST /v1/audio/speech`

Native: `POST /v1/speech`

WebSocket: `wss://tts.thinnest.ai/v1/stream`

Voices

Errors