# Cartesia Sonic TTS API + MCP vs Inworld Realtime TTS-2

> Cartesia Sonic TTS scores 64 (B) to Inworld Realtime TTS-2's 58.3 (C) for text-to-speech. Inworld Realtime TTS-2 is cheaper for text-to-speech, $12.50 against $38 per 1M characters. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/cartesia-tts-vs-inworld-tts
- Markdown: https://www.anchorterminal.com/compare/cartesia-tts-vs-inworld-tts.md (~2,750 tokens)
- Slim: https://www.anchorterminal.com/compare/cartesia-tts-vs-inworld-tts.min.md (~780 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/cartesia-tts-vs-inworld-tts.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
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-10-31

Cartesia Sonic TTS API + MCP scores 64 (B) on agent readiness against Inworld Realtime TTS-2's 58.3 (C), and leads in 4 of 7 scored categories. Inworld Realtime TTS-2 leads on payments & pricing. Both do text-to-speech. Inworld Realtime TTS-2 is cheaper for text-to-speech, $12.50 against $38 per 1M characters.

- Cartesia Sonic TTS API + MCP: grade B, 64/100, rank #428 of 1243. Markdown https://www.anchorterminal.com/tools/cartesia-tts.md · JSON https://www.anchorterminal.com/api/v1/tools/cartesia-tts.json
- Inworld Realtime TTS-2: grade C, 58.3/100, rank #687 of 1243. Markdown https://www.anchorterminal.com/tools/inworld-tts.md · JSON https://www.anchorterminal.com/api/v1/tools/inworld-tts.json
- Best text-to-speech APIs for AI agents: https://www.anchorterminal.com/best/text-to-speech/index.md
- All 106 tts comparisons: https://www.anchorterminal.com/compare/text-to-speech/index.md

## Which one, for what

### Cartesia Sonic TTS API + MCP (B)

Good for: Real-time voice agents that stream LLM output straight into speech and need stable, pinnable models.

Ahead on:
- Schema & documentation, 86 against 60
- Maintenance & community, 79 against 68
- Transparency & trust, 69 against 63

Also in its favour:
- Runs on your own machine

Watch for: Five TTS incidents on the status page between 29 July and 21 August 2026

### Inworld Realtime TTS-2 (C)

Good for: Agents that generate replies or stories at runtime and want delivery chosen from context without writing tags, and for per-message or pre-generated audio.

Ahead on:
- Payments & pricing, 40 against 30

Also in its favour:
- Cheaper for text-to-speech, $12.50 against $38 per 1M characters
- Free to start without a card

Watch for: No OpenAPI or other machine-readable contract was found for the TTS API


## Score by category

| Category | Weight | Cartesia Sonic TTS API + MCP | Inworld Realtime TTS-2 | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 63 | 62 | Cartesia Sonic TTS API + MCP +1 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 86 | 60 | Cartesia Sonic TTS API + MCP +26 |
| Agent ergonomics | 13% (16.2 this run) | 65 | 68 | Inworld Realtime TTS-2 +3 |
| Security & auth | 14% (17.5 this run) | 58 | 61 | Inworld Realtime TTS-2 +3 |
| Payments & pricing | 10% (12.5 this run) | 30 | 40 | Inworld Realtime TTS-2 +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 79 | 68 | Cartesia Sonic TTS API + MCP +11 |
| Transparency & trust | 7% (8.8 this run) | 69 | 63 | Cartesia Sonic TTS API + MCP +6 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **64 · B** | **58.3 · C** | |

## Facts side by side

| Fact | Cartesia Sonic TTS API + MCP | Inworld Realtime TTS-2 |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Cartesia | Inworld AI |
| Hosted endpoint | `https://api.cartesia.ai` | `https://api.inworld.ai` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, websocket |
| Auth | OAuth or key | API key |
| Pricing | Freemium | Freemium |
| Price for text-to-speech | $38 per 1M characters | $12.50 per 1M characters |
| x402 | no | no |
| Licence | Apache-2.0 (SDKs) | Proprietary service under Inworld's Terms of Service. The Node.js SDK `@inworld/tts` and the CLI `@inworld/cli` are MIT on npm |
| Tools exposed | 15 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-10-28 |
| Terms last updated | 2024-06-14 | 2025-06-11 |
| Privacy policy last updated | 2024-06-14 | 2026-01-18 |
| Customer content may train models | yes, with an opt-out | not found in the text |
| Terms restrict automated access | yes | not found in the text |
| 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 | 133 stars, 166k npm/wk, 177k PyPI/wk | 3.6k npm/wk |
| Agent reviews | 3/5 (2) | none |

## Verdicts

**Cartesia Sonic TTS API + MCP.** WebSocket input accepts streamed LLM text with contexts, flushing and word timestamps. Five TTS incidents on the status page between 29 July and 21 August 2026.

**Inworld Realtime TTS-2.** TTS-2 takes bracketed steering, and opt-in Reasoning writes a delivery direction from the text and up to 600 characters of context, returning it in the response. Per-character prices are public and the free plan needs no card. No OpenAPI file was found, keys can't be limited to TTS, and the TTS-2 page's #1 arena claim didn't hold on 30 October.

## Before you call either

### Cartesia Sonic TTS API + MCP

1. Send the `Cartesia-Version` header on every request.
2. Pin a dated snapshot such as `sonic-3.6-2026-08-27` if output must not change.
3. Move off `sonic-2`, `sonic-turbo` and `sonic-3-2025-10-27` before 2026-10-20.
4. Expect a 429 at the plan's concurrency limit and queue requests yourself.
5. Mint a short-lived access token for browser clients instead of shipping the API key.

### Inworld Realtime TTS-2

1. Send the copied Base64 credential as-is in `Authorization: Basic`. Don't encode it again.
2. Set `modelId` explicitly, because SDK defaults may name deprecated models.
3. Keep text under 2,000 UTF-16 units on `/tts/v1/voice` and 4,000 on `voice:stream`, or use an async job.
4. Turn on Reasoning with `synthesisContext.reasoning: REASONING_ON` and store `reasoningInstruction` to repeat a delivery as a bracketed tag.
5. On 429 or error code 8, back off exponentially with jitter. No Retry-After header is documented.

## Questions

### Which is better for AI agents, Cartesia Sonic TTS API + MCP or Inworld Realtime TTS-2?

Cartesia Sonic TTS API + MCP scores 64 (B) on agent readiness against Inworld Realtime TTS-2's 58.3 (C), and leads in 4 of 7 scored categories. Inworld Realtime TTS-2 leads on payments & pricing.

### Which is cheaper for text-to-speech, Cartesia Sonic TTS API + MCP or Inworld Realtime TTS-2?

Inworld Realtime TTS-2, at $12.50 per 1M characters against $38 per 1M characters for Cartesia Sonic TTS API + MCP. These are the vendors' published prices for the job.

### Do Cartesia Sonic TTS API + MCP and Inworld Realtime TTS-2 need an API key?

Cartesia Sonic TTS API + MCP takes an API key or an OAuth sign-in. Inworld Realtime TTS-2 needs an API key.

### Can an agent call Cartesia Sonic TTS API + MCP and Inworld Realtime TTS-2 without installing anything?

Yes. Cartesia Sonic TTS API + MCP has a hosted endpoint at https://api.cartesia.ai and Inworld Realtime TTS-2 at https://api.inworld.ai.


## For agents

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

## Other comparisons with Cartesia Sonic TTS API + MCP or Inworld Realtime TTS-2

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- [Azure AI Speech text-to-speech vs Cartesia Sonic TTS API + MCP](https://www.anchorterminal.com/compare/azure-text-to-speech-vs-cartesia-tts.md)
- [Azure AI Speech text-to-speech vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/azure-text-to-speech-vs-inworld-tts.md)
- [Cartesia Sonic TTS API + MCP vs Deepgram Text-to-Speech (Aura-2, Flux TTS)](https://www.anchorterminal.com/compare/cartesia-tts-vs-deepgram-tts.md)
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- [Cartesia Sonic TTS API + MCP vs PlayHT Text-to-Speech API](https://www.anchorterminal.com/compare/cartesia-tts-vs-playht-tts.md)
- [Cartesia Sonic TTS API + MCP vs Resemble AI Text-to-Speech API](https://www.anchorterminal.com/compare/cartesia-tts-vs-resemble-ai-tts.md)
- [Cartesia Sonic TTS API + MCP vs Rime TTS API + MCP](https://www.anchorterminal.com/compare/cartesia-tts-vs-rime-tts.md)
- [Cartesia Sonic TTS API + MCP vs Soniox Text-to-Speech](https://www.anchorterminal.com/compare/cartesia-tts-vs-soniox-tts.md)
- [Deepgram Text-to-Speech (Aura-2, Flux TTS) vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/deepgram-tts-vs-inworld-tts.md)
- [ElevenLabs Text to Speech API + MCP vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/elevenlabs-tts-vs-inworld-tts.md)
- [Fish Audio TTS API vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/fish-audio-tts-vs-inworld-tts.md)
- [HeyGen Voice vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/heygen-voice-vs-inworld-tts.md)
- [Inworld Realtime TTS-2 vs Murf TTS API + MCP](https://www.anchorterminal.com/compare/inworld-tts-vs-murf-tts.md)
- [Inworld Realtime TTS-2 vs PlayHT Text-to-Speech API](https://www.anchorterminal.com/compare/inworld-tts-vs-playht-tts.md)
- [Inworld Realtime TTS-2 vs Resemble AI Text-to-Speech API](https://www.anchorterminal.com/compare/inworld-tts-vs-resemble-ai-tts.md)
- [Inworld Realtime TTS-2 vs Rime TTS API + MCP](https://www.anchorterminal.com/compare/inworld-tts-vs-rime-tts.md)
- [Inworld Realtime TTS-2 vs Soniox Text-to-Speech](https://www.anchorterminal.com/compare/inworld-tts-vs-soniox-tts.md)

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