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Realtime

Transcription Sessions

Create transcription session
Deprecated
POST/realtime/transcription_sessions
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TranscriptionSessionCreateResponse object { client_secret, input_audio_format, input_audio_transcription, 2 more }

A new Realtime transcription session configuration.

When a session is created on the server via REST API, the session object also contains an ephemeral key. Default TTL for keys is 10 minutes. This property is not present when a session is updated via the WebSocket API.

client_secret: object { expires_at, value }

Ephemeral key returned by the API. Only present when the session is created on the server via REST API.

expires_at: number

Timestamp for when the token expires. Currently, all tokens expire after one minute.

formatunixtime
value: string

Ephemeral key usable in client environments to authenticate connections to the Realtime API. Use this in client-side environments rather than a standard API token, which should only be used server-side.

input_audio_format: optional string

The format of input audio. Options are pcm16, g711_ulaw, or g711_alaw.

input_audio_transcription: optional object { language, model, prompt }

Configuration of the transcription model.

language: optional string

The language of the input audio.

model: optional string or "whisper-1" or "gpt-4o-mini-transcribe" or "gpt-4o-mini-transcribe-2025-12-15" or 3 more

The model used for transcription. Current options are whisper-1, gpt-4o-mini-transcribe, gpt-4o-mini-transcribe-2025-12-15, gpt-4o-transcribe, gpt-4o-transcribe-diarize, and gpt-realtime-whisper.

One of the following:
string
"whisper-1" or "gpt-4o-mini-transcribe" or "gpt-4o-mini-transcribe-2025-12-15" or 3 more

The model used for transcription. Current options are whisper-1, gpt-4o-mini-transcribe, gpt-4o-mini-transcribe-2025-12-15, gpt-4o-transcribe, gpt-4o-transcribe-diarize, and gpt-realtime-whisper.

One of the following:
"whisper-1"
"gpt-4o-mini-transcribe"
"gpt-4o-mini-transcribe-2025-12-15"
"gpt-4o-transcribe"
"gpt-4o-transcribe-diarize"
"gpt-realtime-whisper"
prompt: optional string

The prompt configured for input audio transcription, when present.

modalities: optional array of "text" or "audio"

The set of modalities the model can respond with. To disable audio, set this to [“text”].

One of the following:
"text"
"audio"
turn_detection: optional object { prefix_padding_ms, silence_duration_ms, threshold, type }

Configuration for turn detection. Can be set to null to turn off. Server VAD means that the model will detect the start and end of speech based on audio volume and respond at the end of user speech.

prefix_padding_ms: optional number

Amount of audio to include before the VAD detected speech (in milliseconds). Defaults to 300ms.

silence_duration_ms: optional number

Duration of silence to detect speech stop (in milliseconds). Defaults to 500ms. With shorter values the model will respond more quickly, but may jump in on short pauses from the user.

threshold: optional number

Activation threshold for VAD (0.0 to 1.0), this defaults to 0.5. A higher threshold will require louder audio to activate the model, and thus might perform better in noisy environments.

type: optional string

Type of turn detection, only server_vad is currently supported.