> ## Documentation Index > Fetch the complete documentation index at: https://aircaps.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # Models > What each model does and when to use it.
ModelWhat it does
[**A5S Async v1**](#a5s-async-v1)\ `a5s-async-v1` Recorded audio (0.1 s to 10 h) → a transcript with speaker labels, word timestamps and subtitles.\ REST, async jobs
[**A5S Small V2 Streaming**](#a5s-small-v2-streaming)\ `a5s-small-v2-streaming` Live audio → captions as people speak, with optional speaker labels and names.\ WebSocket
[**AirCaps Diarization-v1**](#aircaps-diarization-v1)\ `aircaps-diarization-v1` Recorded audio (0.1 s to 6 h) → who spoke when: speaker segments as JSON or RTTM.\ REST, async jobs · enabled on request
[**AirCaps Speaker ID-v1**](#aircaps-speaker-id-v1)\ `aircaps-speaker-id-v1` A clip (0.5 s to 2 min) → a score for each of your enrolled speakers.\ REST, synchronous · enabled on request
## A5S Async v1 `a5s-async-v1` · REST · [batch guide](https://aircaps.ai/docs/guides/async-transcription.md) · [benchmarks](https://aircaps.ai/research/a5s-async) * Recorded audio in any common format, from 0.1 s to 10 hours. * Speaker labels (`speaker_0`, `speaker_1`, …), word timestamps, utterances, SRT/VTT subtitles. * Optional key terms: up to 60 per transcript help it recognize names and jargon (`keyterms`, see [Key terms](https://aircaps.ai/docs/guides/async-transcription.md#key-terms)). * Optional speaker names from your enrolled voices (`speaker_identification`, with AirCaps Speaker ID-v1 enabled). See [Speaker names](https://aircaps.ai/docs/guides/async-transcription.md#speaker-names). * English only: `language_code` is `en` or a regional English code such as `en-US`, `en-GB` or `en-IN`; use the one that matches the speakers' locale or accent. * Text is verbatim and lowercase without punctuation (apostrophes are kept, as in "let's"); disfluencies ("uh", "um") are kept. ## A5S Small V2 Streaming `a5s-small-v2-streaming` · WebSocket · [streaming guide](https://aircaps.ai/docs/guides/streaming.md) · [benchmarks](https://aircaps.ai/research/a5s-small-v2) > [!NOTE] > > Formerly A5S v2 Streaming, with id `a5s-v2-streaming`. The old id still works for now: a session or request that names it gets a `model_deprecated` warning (in `ready.warnings` on the WebSocket). It will be removed soon, so use `a5s-small-v2-streaming`. * Live 16 kHz mono PCM16 audio in, partial and final text out as people speak. * Punctuated, cased text. * Optional live speaker labels (`diarization: true`): utterances and words labelled `speaker_0`, `speaker_1`, …. See [Speaker labels](https://aircaps.ai/docs/guides/streaming.md#speaker-labels). * Optional live speaker names from your enrolled voices (`speaker_identification`, with speaker labels on and AirCaps Speaker ID-v1 enabled). See [Speaker names](https://aircaps.ai/docs/guides/streaming.md#speaker-names). * Optional key terms to bias recognition toward names and jargon (`custom_vocabulary`, see [Key terms](https://aircaps.ai/docs/guides/streaming.md#key-terms)). * English only: the start message's `language` accepts only `en`. * Sessions last up to 30 minutes (up to 4 hours on request). ## AirCaps Diarization-v1 `aircaps-diarization-v1` · REST · [diarization guide](https://aircaps.ai/docs/guides/diarization.md) · [benchmarks](https://aircaps.ai/research/diarization) · enabled on request * Who spoke when, with no transcript: speaker segments (`speaker_0`, `speaker_1`, …) with millisecond times, overlapping speech included, plus each speaker's speaking time. * Finds the number of speakers itself. Works from the voices, not the words: no `language_code`. * Recorded audio in any common format, from 0.1 s to 6 hours. Results as JSON or [RTTM](https://aircaps.ai/docs/api-reference/diarization-rttm.md). * Enabled per account: [talk to sales](https://aircaps.ai/contact) for access. ## AirCaps Speaker ID-v1 `aircaps-speaker-id-v1` · REST, synchronous · [speaker ID guide](https://aircaps.ai/docs/guides/speaker-id.md) · [evaluation](https://aircaps.ai/research/speaker-id) · enabled on request * Recognize enrolled people by voice. Enroll each person with one or more clips, then send a clip and get back a score for every enrolled speaker, best first. * Also names the speakers of A5S Async v1 transcripts (`speaker_identification` on [create a transcript](https://aircaps.ai/docs/guides/async-transcription.md#speaker-names)) and of A5S Small V2 Streaming sessions with speaker labels ([live speaker names](https://aircaps.ai/docs/guides/streaming.md#speaker-names)). * Synchronous: one clip per request, 0.5 s to 2 minutes; the scores are the response. No jobs, no polling. * You set the threshold: scores are similarities from -1 to 1, with no accept/reject decision. The [guide](https://aircaps.ai/docs/guides/speaker-id.md#scores-and-thresholds) has measured score ranges to start from. * The whole clip is compared as given. Crop clips to one person's speech first (for example with [AirCaps Diarization-v1](https://aircaps.ai/docs/guides/diarization.md) or a transcript's utterances). * Works from the voice, not the words: no `language_code`. * Enabled per account: [talk to sales](https://aircaps.ai/contact) for access. ## Choosing | You have | Use | | - | - | | Recordings, uploads, meeting files | A5S Async v1 | | A live microphone or call that needs captions now | A5S Small V2 Streaming | | Live audio that needs speaker labels as it happens | A5S Small V2 Streaming with `diarization: true` | | The most accurate speaker-labelled transcript of a recording | A5S Async v1 | | Only who spoke when (speaker segments, no text), or speakers for a transcript you already have | AirCaps Diarization-v1 | | Which known person is speaking in a clip (names instead of `speaker_0`, `speaker_1`) | AirCaps Speaker ID-v1 | ## Languages The transcription models support English today: `language_code` (A5S Async v1) takes `en` or a regional English code (`en-US`, `en-GB`, `en-IN`, …), and `language` (A5S Small V2 Streaming) takes `en`. **Multilingual support is planned and will be available soon.** AirCaps Diarization-v1 and AirCaps Speaker ID-v1 work from the voice and take no language. ## Access Accounts can use A5S Async v1 and A5S Small V2 Streaming by default; an account may be limited to one of them. AirCaps Diarization-v1 and AirCaps Speaker ID-v1 are enabled per account on request. Requests to a model your account can't use return `403 model_access_denied` (streaming: an `error` message with that code, then close code `4403`). `GET /v1/account` shows `enabled` for each model. To get access, [talk to sales](https://aircaps.ai/contact). `GET /v1/models` lists the models. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.