# AssemblyAI Speech-to-Text (Universal) vs Deepgram Speech-to-Text (Nova-3, Flux)

> Deepgram Speech-to-Text (Nova-3, Flux) has a score of 70.6 (BB) against AssemblyAI Speech-to-Text (Universal)'s 67 (B). Both do speech stt. The largest gap is security & auth, 15 points. Category scores, facts, verdicts and agent notes side by side.

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- Updated: 2026-10-04

Deepgram Speech-to-Text (Nova-3, Flux) has a score of 70.6 (BB) against AssemblyAI Speech-to-Text (Universal)'s 67 (B). Both do speech stt. The largest gap is security & auth, 15 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
- Deepgram Speech-to-Text (Nova-3, Flux): grade BB, 70.6/100, rank #94 of 452. Markdown https://www.anchorterminal.com/tools/deepgram-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/deepgram-stt.json

## Which one, for what

Pick AssemblyAI Speech-to-Text (Universal) for reliability (+5), agent ergonomics (+5).

Pick Deepgram Speech-to-Text (Nova-3, Flux) for security & auth (+15).

## Score by category

| Category | Weight | AssemblyAI Speech-to-Text (Universal) | Deepgram Speech-to-Text (Nova-3, Flux) | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 70 | 65 | AssemblyAI Speech-to-Text (Universal) +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 95 | 95 | even |
| Agent ergonomics | 13% (16.2 this run) | 80 | 75 | AssemblyAI Speech-to-Text (Universal) +5 |
| Security & auth | 14% (17.5 this run) | 50 | 65 | Deepgram Speech-to-Text (Nova-3, Flux) +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 | 80 | even |
| Transparency & trust | 7% (8.8 this run) | 78 | 75 | AssemblyAI Speech-to-Text (Universal) +3 |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **67 · B** | **70.6 · BB** | |

## Facts side by side

| Fact | AssemblyAI Speech-to-Text (Universal) | Deepgram Speech-to-Text (Nova-3, Flux) |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | AssemblyAI | Deepgram |
| Hosted endpoint | `https://api.assemblyai.com/v2` | `https://api.deepgram.com/v1` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP, stdio, SSE (legacy) |
| 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 | 2026-09-29 |
| Popularity | 213 stars, 600k npm/wk, 738k PyPI/wk | 468 stars, 1.1M npm/wk, 805k 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.

**Deepgram Speech-to-Text (Nova-3, Flux).** Flux streams with model-level end-of-turn detection, so a voice agent needs no separate VAD. Training on audio is the default and the opt-out is a per-request flag.

## 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

### Deepgram Speech-to-Text (Nova-3, Flux)

1. Add `mip_opt_out=true` to every request that carries customer audio
2. Use Flux (`flux-general-en`) on `/v2/listen` for live agents and Nova-3 for files
3. Back off exponentially on 429. The concurrency limit is per project
4. Pass `callback` for long files so the request doesn't hit the 10-minute processing timeout
5. Mint keys with an expiry for short-lived jobs

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