> ## Documentation Index
> Fetch the complete documentation index at: https://docs.modulate.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Speech-to-text Transcription

> Speech-to-text APIs — multilingual batch transcription, fast English-only batch, fast multilingual batch, real-time streaming, and low-latency English and multilingual streaming.

Modulate offers six speech-to-text endpoints. Pick the one that matches your latency, language, and feature needs.

| | Multilingual (batch) | Multilingual (streaming) | English Fast (batch) | English Fast (streaming) | Multilingual Fast (batch) | Multilingual Fast (streaming) |
| - | - | - | - | - | - | - |
| **Use case** | Transcription with rich metadata | Real-time transcription | Fast English-only transcription | Low-latency English real-time transcription | Fast multilingual transcription  Real-time multilingual transcription | Real-time multilingual transcription |
| **Protocol** | HTTP POST | WebSocket | HTTP POST | WebSocket | HTTP POST | WebSocket |
| **Languages** | Multilingual | Multilingual | English only | English only | Multilingual | Multilingual (25, auto-identified) |
| **Language declaration** | ✓ (optional `language` hint) | ✓ (optional `language` hint) | — | — | ✓ (optional `language`, skips auto-detection) | — (always auto-identified) |
| **Speaker diarization** | ✓ | ✓ | ✓ (opt-in `speaker_diarization`) | ✓ (opt-in `diarize`, 10 speakers) | — | ✓ (opt-in `diarize`, 4 speakers) |
| **Word-level timings** | — | — | ✓ (opt-in `time_stamps`) | — | — | — |
| **Emotion / accent detection** | ✓ | ✓ | — | — | — | — |
| **PII/PHI tagging** | ✓ | ✓ | — | — | — | — |
| **Partial transcripts during streaming** | — | ✓ (opt-in `partial_results`) | — | ✓ (every \~1.5 s) | — | ✓ |

For a side-by-side comparison with the other Modulate capabilities, see [Which API should I use?](/guides/which-api).

## Authentication

Batch endpoints use the `X-API-Key` header. Streaming endpoints use an `api_key` query parameter at connection time. See [Authentication and rate limits](/guides/authentication).


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