# Diarization

Speaker diarization partitions transcribed speech by speaker - answering "who spoke when". When enabled, each piece of transcribed text is labelled with a `speaker_id` so you can tell participants apart in a conversation.

Diarization is available on the [Prerecorded](/speech-to-text/prerecorded/) and [Realtime](/speech-to-text/realtime/) APIs. It is not available on the [Turns](/speech-to-text/turns/) API.

## Enabling Diarization

Set the `diarize` query parameter to `true`. Optionally cap the number of distinct speakers with `max_speakers` (1-4); leave it unset to let the server determine the count automatically.

```
?diarize=true&max_speakers=2
```

## Speaker IDs

Each speaker is identified by an integer `speaker_id`, starting at `0`. IDs are assigned in the order speakers are first heard and remain stable for the duration of a session.

:::note[Anonymous labels]
Speaker IDs are anonymous labels, not identities. `speaker_id: 0` is simply "the first speaker heard" - diarization does not recognise *who* a person is across sessions.
:::

## In the Response

On prerecorded, the response is split into per-speaker `segments`, each with its own `speaker_id` and text. On realtime, each transcript message carries the `speaker_id` of its dominant speaker. See the API reference for [Prerecorded](/api/speech-to-text/prerecorded/) and [Realtime](/api/speech-to-text/realtime/) for the full response fields.