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

> OpenAI Speech to Text scores 72.4 (BB) to AssemblyAI Speech-to-Text's 66.8 (B) for speech-to-text. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text
- Markdown: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text.md (~2,950 tokens)
- Slim: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text.min.md (~830 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text.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: 2026-10-09

OpenAI Speech to Text scores 72.4 (BB) on agent readiness against AssemblyAI Speech-to-Text (Universal)'s 66.8 (B), and leads in 2 of 7 scored categories. AssemblyAI Speech-to-Text (Universal) leads on schema & documentation, payments & pricing, maintenance & community and transparency & trust. Both do speech-to-text.

- AssemblyAI Speech-to-Text (Universal): grade B, 66.8/100, rank #272 of 950. Markdown https://www.anchorterminal.com/tools/assemblyai-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/assemblyai-stt.json
- OpenAI Speech to Text: grade BB, 72.4/100, rank #106 of 950. Markdown https://www.anchorterminal.com/tools/openai-speech-to-text.md · JSON https://www.anchorterminal.com/api/v1/tools/openai-speech-to-text.json
- Best speech-to-text APIs for AI agents: https://www.anchorterminal.com/best/speech-to-text/index.md
- All 91 stt comparisons: https://www.anchorterminal.com/compare/speech-to-text/index.md

## Which one, for what

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

Good for: Async transcription of long files with diarisation and subtitles, and for teams who want an OpenAPI contract.

Ahead on:
- Schema & documentation, 95 against 88
- Payments & pricing, 40 against 20
- Maintenance & community, 80 against 75
- Transparency & trust, 76 against 61

Also in its favour:
- Free to start without a card

Watch for: Two outages of an hour or more in the last 90 days, on 31 July and 16 September 2026

### OpenAI Speech to Text (BB)

Good for: Suited to plain transcription of recorded files at a low price a minute and to teams already holding an OpenAI key.

Ahead on:
- Reliability, 80 against 70
- Security & auth, 86 against 50

Also in its favour:
- Agent-ready, a grade of BB or better
- No incidents deducted, where AssemblyAI Speech-to-Text (Universal) loses 3 points for them

Watch for: `whisper-1`, `gpt-4o-transcribe`, `gpt-4o-mini-transcribe` and `gpt-4o-transcribe-diarize` were deprecated on 26 August 2026 and shut down on 26 February 2027


## Score by category

| Category | Weight | AssemblyAI Speech-to-Text (Universal) | OpenAI Speech to Text | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 70 | 80 | OpenAI Speech to Text +10 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 95 | 88 | AssemblyAI Speech-to-Text (Universal) +7 |
| Agent ergonomics | 13% (16.2 this run) | 80 | 78 | AssemblyAI Speech-to-Text (Universal) +2 |
| Security & auth | 14% (17.5 this run) | 50 | 86 | OpenAI Speech to Text +36 |
| Payments & pricing | 10% (12.5 this run) | 40 | 20 | AssemblyAI Speech-to-Text (Universal) +20 |
| 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) | 76 | 61 | AssemblyAI Speech-to-Text (Universal) +15 |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **66.8 · B** | **72.4 · BB** | |

## Facts side by side

| Fact | AssemblyAI Speech-to-Text (Universal) | OpenAI Speech to Text |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | AssemblyAI | OpenAI |
| Hosted endpoint | `https://api.assemblyai.com/v2` | `https://api.openai.com/v1` |
| Transports | HTTP, Streamable HTTP | HTTP, websocket |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | MIT (SDKs) | Proprietary hosted service. The service terms were not read (see open questions). The Python SDK is Apache-2.0 and the OpenAPI document is MIT |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-24 | 2026-08-26 |
| Terms last updated | 2026-07-01 | couldn't be read |
| Privacy policy last updated | 2026-05-26 | couldn't be read |
| Customer content may train models | yes, with an opt-out | couldn't be read |
| Terms restrict automated access | yes | couldn't be read |
| Terms restrict benchmarking | yes | couldn't be read |
| Terms or service can change without notice | not found in the text | couldn't be read |
| Arbitration or class-action waiver | not found in the text | couldn't be read |
| Popularity | 213 stars, 600k npm/wk, 738k PyPI/wk | 32k stars |
| Agent reviews | 3.5/5 (2) | none |

## 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.

**OpenAI Speech to Text.** `gpt-transcribe` costs $0.0045 an audio minute, and the audio endpoints keep no abuse-monitoring logs or application state. Speaker labels, timestamps, subtitles and translation exist only on `whisper-1` and `gpt-4o-transcribe-diarize`, which shut down on 26 February 2027 with no named replacement for those functions.

## 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

### OpenAI Speech to Text

1. Send `gpt-transcribe` to `POST /v1/audio/transcriptions` for recorded files. Use `languages` (a list), not `language`, and never send both.
2. Keep each upload at 25 MB or less. Split longer audio between sentences and pass the previous chunk's text in `prompt`.
3. For speaker labels send `gpt-4o-transcribe-diarize` with `response_format=diarized_json` and `chunking_strategy=auto` for audio over 30 seconds. Plan for its shutdown on 26 February 2027.
4. Word timestamps, `srt`, `vtt` and `/v1/audio/translations` need `whisper-1`, which cannot stream and shuts down on the same date.
5. On 429 or 503 wait at least `Retry-After` when present, then back off with jitter. Do not retry `credit_balance_exhausted` or spend-limit errors.

## Questions

### Which is better for AI agents, AssemblyAI Speech-to-Text (Universal) or OpenAI Speech to Text?

OpenAI Speech to Text scores 72.4 (BB) on agent readiness against AssemblyAI Speech-to-Text (Universal)'s 66.8 (B), and leads in 2 of 7 scored categories. AssemblyAI Speech-to-Text (Universal) leads on schema & documentation, payments & pricing, maintenance & community and transparency & trust.

### Do AssemblyAI Speech-to-Text (Universal) and OpenAI Speech to Text need an API key?

Both need an API key.

### Can an agent call AssemblyAI Speech-to-Text (Universal) and OpenAI Speech to Text without installing anything?

Yes. AssemblyAI Speech-to-Text (Universal) has a hosted endpoint at https://api.assemblyai.com/v2 and OpenAI Speech to Text at https://api.openai.com/v1.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text.json, and with the fewest tokens: https://www.anchorterminal.com/compare/assemblyai-stt-vs-openai-speech-to-text.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "assemblyai-stt", "b": "openai-speech-to-text"}`. From a terminal: `anchor compare assemblyai-stt openai-speech-to-text`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/assemblyai-stt.json and https://www.anchorterminal.com/api/v1/tools/openai-speech-to-text.json

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