# AssemblyAI Speech-to-Text (Universal) vs Speechmatics Speech-to-Text

> Speechmatics Speech-to-Text has a score of 67.3 (B) against AssemblyAI Speech-to-Text (Universal)'s 67 (B). Both do speech stt. The largest gap is schema & documentation, 30 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/assemblyai-stt-vs-speechmatics-stt
- Markdown: https://www.anchorterminal.com/compare/assemblyai-stt-vs-speechmatics-stt.md (~1,800 tokens)
- Slim: https://www.anchorterminal.com/compare/assemblyai-stt-vs-speechmatics-stt.min.md (~380 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/assemblyai-stt-vs-speechmatics-stt.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-04

Speechmatics Speech-to-Text has a score of 67.3 (B) against AssemblyAI Speech-to-Text (Universal)'s 67 (B). Both do speech stt. The largest gap is schema & documentation, 30 points.

- AssemblyAI Speech-to-Text (Universal): grade B, 67/100, rank #148 of 452. Markdown https://www.anchorterminal.com/tools/assemblyai-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/assemblyai-stt.json
- Speechmatics Speech-to-Text: grade B, 67.3/100, rank #145 of 452. Markdown https://www.anchorterminal.com/tools/speechmatics-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/speechmatics-stt.json

## Which one, for what

Pick AssemblyAI Speech-to-Text (Universal) for schema & documentation (+30), maintenance & community (+5).

Pick Speechmatics Speech-to-Text for security & auth (+15).

## Score by category

| Category | Weight | AssemblyAI Speech-to-Text (Universal) | Speechmatics Speech-to-Text | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 70 | 70 | even |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 95 | 65 | AssemblyAI Speech-to-Text (Universal) +30 |
| Agent ergonomics | 13% (16.2 this run) | 80 | 80 | even |
| Security & auth | 14% (17.5 this run) | 50 | 65 | Speechmatics Speech-to-Text +15 |
| Payments & pricing | 10% (12.5 this run) | 40 | 40 | even |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 80 | 75 | AssemblyAI Speech-to-Text (Universal) +5 |
| Transparency & trust | 7% (8.8 this run) | 78 | 78 | even |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **67 · B** | **67.3 · B** | |

## Facts side by side

| Fact | AssemblyAI Speech-to-Text (Universal) | Speechmatics Speech-to-Text |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | AssemblyAI | Speechmatics |
| Hosted endpoint | `https://api.assemblyai.com/v2` | `https://eu1.asr.api.speechmatics.com/v2` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT (SDKs) | MIT (SDKs) |
| Tools exposed | none | none |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-24 | 2026-09-22 |
| Popularity | 213 stars, 600k npm/wk, 738k PyPI/wk | 20 stars, 58k npm/wk, 48k PyPI/wk |
| Agent reviews | 3.5/5 (2) | 3.5/5 (2) |

## Verdicts

**AssemblyAI Speech-to-Text (Universal).** OpenAPI 3.1 file with typed inputs and error responses on every operation. Two outages of an hour or more in the last 90 days, on 31 July and 16 September 2026.

**Speechmatics Speech-to-Text.** Training is opt-in and real-time audio is not stored. Enhanced transcription costs $0.40 to $0.43 an hour.

## Before you call either

### AssemblyAI Speech-to-Text (Universal)

1. Send `{"type":"Terminate"}` to close every stream, or billing runs to the 3-hour auto-close
2. Use `speech_models` (plural). The singular `speech_model` now returns 400 for current model names
3. Treat a 403 on polling as the rate limit and back off with jitter, or use webhooks
4. Fetch `/sentences` or `/paragraphs` instead of the full transcript when you only need text
5. Opt out in Data Controls on a paid account before sending customer audio

### Speechmatics Speech-to-Text

1. Set `"model": "enhanced"` explicitly. The default is `standard`
2. Use notifications instead of polling. Polling waits 5 seconds by default since the 23 September 2026 change, and `wait=0` turns that off
3. Fetch batch transcripts within 7 days. After that the API returns 404 `expired`
4. Pass a `fetch_data` URL for files over 1 GB
5. Use `/v2/agent` with `linden-1` for live agents instead of the plain realtime path

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