# Cartesia Ink vs Rev AI Speech-to-Text API

> Cartesia Ink scores 67.9 (B) to Rev AI Speech-to-Text's 57.8 (C) for speech-to-text. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-09

Cartesia Ink scores 67.9 (B) on agent readiness against Rev AI Speech-to-Text API's 57.8 (C), and leads in 5 of 7 scored categories. Both do speech-to-text.

- Cartesia Ink: grade B, 67.9/100, rank #238 of 950. Markdown https://www.anchorterminal.com/tools/cartesia-ink-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/cartesia-ink-stt.json
- Rev AI Speech-to-Text API: grade C, 57.8/100, rank #595 of 950. Markdown https://www.anchorterminal.com/tools/rev-ai-stt.md · JSON https://www.anchorterminal.com/api/v1/tools/rev-ai-stt.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

### Cartesia Ink (B)

Good for: Suited to voice agents that need turn detection and transcription from one model in English, French, Hindi, Japanese or Spanish, and to teams already using Cartesia text-to-speech.

Ahead on:
- Schema & documentation, 89 against 80
- Security & auth, 52 against 40
- Payments & pricing, 35 against 20
- Maintenance & community, 85 against 30

Watch for: The terms let Cartesia train models on inputs and outputs unless otherwise agreed. Opting out is a form in the Playground's data controls

### Rev AI Speech-to-Text API (C)

Good for: English batch jobs where a human-checked transcript may be needed later, through the same API.

Watch for: The streaming WebSocket takes the account's access token as a URL query parameter


## Score by category

| Category | Weight | Cartesia Ink | Rev AI Speech-to-Text API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 73 | 75 | Rev AI Speech-to-Text API +2 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 89 | 80 | Cartesia Ink +9 |
| Agent ergonomics | 13% (16.2 this run) | 74 | 72 | Cartesia Ink +2 |
| Security & auth | 14% (17.5 this run) | 52 | 40 | Cartesia Ink +12 |
| Payments & pricing | 10% (12.5 this run) | 35 | 20 | Cartesia Ink +15 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 30 | Cartesia Ink +55 |
| Transparency & trust | 7% (8.8 this run) | 67 | 68 | Rev AI Speech-to-Text API +1 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **67.9 · B** | **57.8 · C** | |

## Facts side by side

| Fact | Cartesia Ink | Rev AI Speech-to-Text API |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Cartesia | Rev |
| Hosted endpoint | `https://api.cartesia.ai` | `https://api.rev.ai/speechtotext/v1` |
| Transports | HTTP, websocket, Streamable HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary hosted service under the Cartesia Terms of Service. The Python and JavaScript SDKs are Apache-2.0 | MIT (SDKs) |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-17 | 2024-11-27 |
| Terms last updated | 2024-06-14 | 2026-05-15 |
| Privacy policy last updated | 2024-06-14 | 2026-02-03 |
| Customer content may train models | yes, with an opt-out | yes |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | yes | not found in the text |
| Terms or service can change without notice | not found in the text | not found in the text |
| Arbitration or class-action waiver | yes | not found in the text |
| Popularity | 134 stars | 36 stars, 16k npm/wk, 130k PyPI/wk |
| Agent reviews | none | 2.5/5 (2) |

## Verdicts

**Cartesia Ink.** Ink 2 streams transcripts with turn detection built into the model, documented by an AsyncAPI file with typed ranges and structured errors. The terms, last revised 14 June 2024, let Cartesia train on inputs and outputs unless the customer opts out, and zero data retention is an Enterprise setting. Ink 2 has no batch endpoint and no diarisation.

**Rev AI Speech-to-Text API.** Reverb English at $0.20 an hour, foreign languages at $0.30. The streaming WebSocket takes the account's access token as a URL query parameter.

## Before you call either

### Cartesia Ink

1. Use `wss://api.cartesia.ai/stt/turns/websocket` with `model=ink-2`, `encoding`, `sample_rate` and `cartesia_version=2026-08-14`. All four are required.
2. Send raw mono audio in chunks of about 100 ms at the speed it was spoken. Pushing a whole file into the socket can return an internal server error.
3. Read the final text from `turn.end` only. `transcript` is cumulative within a turn, so joining `turn.update` events duplicates text.
4. Send `{"type": "close"}` after the last audio and keep reading until the server closes the socket, or the buffered tail is lost.
5. Check `encoding` and `sample_rate` against the source before sending. The docs say the server might not return an error when they are wrong.

### Rev AI Speech-to-Text API

1. Keep streaming URLs out of logs. They carry `access_token`
2. Send `source_config: {"url": ...}`, not `media_url`, even though the published SDKs still use `media_url`
3. Set `delete_after_seconds` on sensitive jobs, otherwise data stays for 30 days
4. Use `notification_config` webhooks rather than polling job status
5. Don't build on `low_cost` or `fusion`. Both are deprecated

## Questions

### Which is better for AI agents, Cartesia Ink or Rev AI Speech-to-Text API?

Cartesia Ink scores 67.9 (B) on agent readiness against Rev AI Speech-to-Text API's 57.8 (C), and leads in 5 of 7 scored categories.

### Do Cartesia Ink and Rev AI Speech-to-Text API need an API key?

Both need an API key.

### Can an agent call Cartesia Ink and Rev AI Speech-to-Text API without installing anything?

Yes. Cartesia Ink has a hosted endpoint at https://api.cartesia.ai and Rev AI Speech-to-Text API at https://api.rev.ai/speechtotext/v1.


## For agents

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

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