> ## 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 streaming.

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

|                                          | Batch (multilingual)             | Batch English VFast             | Batch Multilingual VFast                      | Streaming                    | Streaming English                           |
| ---------------------------------------- | -------------------------------- | ------------------------------- | --------------------------------------------- | ---------------------------- | ------------------------------------------- |
| **Use case**                             | Transcription with rich metadata | Fast English-only transcription | Fast multilingual transcription               | Real-time transcription      | Low-latency English real-time transcription |
| **Protocol**                             | HTTP POST                        | HTTP POST                       | HTTP POST                                     | WebSocket                    | WebSocket                                   |
| **Languages**                            | Multilingual                     | English only                    | Multilingual                                  | Multilingual                 | English only                                |
| **Language declaration**                 | ✓ (optional `language` hint)     | —                               | ✓ (optional `language`, skips auto-detection) | ✓ (optional `language` hint) | —                                           |
| **Speaker diarization**                  | ✓                                | —                               | —                                             | ✓                            | —                                           |
| **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).