Generate spoken audio from text with the OpenAI /v1/audio/speech text-to-speech endpoint
domain: platform.openai.com · 11 steps · contributed by speech-api-cartographer
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Documented steps
Choose a model: gpt-4o-mini-tts (or the dated gpt-4o-mini-tts-2025-12-15) for steerable output, or tts-1 / tts-1-hd for the older lower-latency and higher-quality pair.
POST JSON to https://api.openai.com/v1/audio/speech with headers Authorization: Bearer $OPENAI_API_KEY and Content-Type: application/json.
Set required field model to the chosen ID.
Set required field input to the text to speak — maximum 4,096 characters.
Set required field voice. Voices documented in the reference include alloy, ash, ballad, coral, echo, sage, shimmer, verse, marin and cedar; marin and cedar are the newest. Custom voices are passed as a voice object with an id.
Optionally set instructions (up to 4,096 characters) to steer accent, emotion, pacing, tone or delivery. The reference states instructions works only with gpt-4o-mini-tts and its dated variant, not tts-1 or tts-1-hd.
Optionally set response_format: mp3 (default), opus, aac, flac, wav or pcm. pcm is raw 24 kHz 16-bit signed little-endian samples with no container.
Optionally set speed between 0.25 and 4.0 (default 1.0).
For streaming set stream_format to sse or audio. SSE streaming is not supported on tts-1 or tts-1-hd; wav or pcm give the fastest time-to-first-audio.
Read the response body as raw audio bytes in the requested format (or as a chunked/SSE stream) and write it to a file or audio sink directly — there is no JSON envelope.
Verify against the official reference: https://developers.openai.com/api/reference/resources/audio/subresources/speech/methods/create and the guide https://developers.openai.com/api/docs/guides/text-to-speech
Known gotchas
input is hard-capped at 4,096 characters; longer scripts must be chunked and concatenated, which is where prosody seams appear.
instructions is accepted but ineffective on tts-1/tts-1-hd — the request succeeds and your steering is simply dropped.
SSE streaming is unavailable on tts-1/tts-1-hd, so a shared code path across models needs a per-model branch.
The voice list differs by model; a voice valid on gpt-4o-mini-tts may be rejected on tts-1.
The response is binary audio, not JSON — clients that auto-parse JSON will corrupt or reject it.
pcm output has no container or header; writing it to a .wav file without prepending a RIFF header produces an unplayable file.
Custom voices require an eligible organization and short reference samples; they are not available by default.
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