# Amazon Polly vs Inworld Realtime TTS-2

> Amazon Polly scores 73.6 (BB) to Inworld Realtime TTS-2's 58.3 (C) for text-to-speech. Prices, MCP, x402, uptime and agent notes side by side.

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Amazon Polly scores 73.6 (BB) on agent readiness against Inworld Realtime TTS-2's 58.3 (C), and leads in 5 of 7 scored categories. Inworld Realtime TTS-2 leads on payments & pricing and maintenance & community. Both do text-to-speech.

- Amazon Polly: grade BB, 73.6/100, rank #91 of 1243. Markdown https://www.anchorterminal.com/tools/amazon-polly.md · JSON https://www.anchorterminal.com/api/v1/tools/amazon-polly.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

### Amazon Polly (BB)

Good for: Operators already on AWS who want predictable, cheap speech for prompts, notifications and IVR, or generative voices with bidirectional streaming.

Ahead on:
- Reliability, 80 against 62
- Schema & documentation, 90 against 60
- Agent ergonomics, 82 against 68
- Security & auth, 83 against 61
- Transparency & trust, 80 against 63

Also in its favour:
- Agent-ready, a grade of BB or better

Watch for: AWS may store and use text to improve the service, possibly outside the Region, unless the organisation sets an AI services opt-out policy

### 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
- Maintenance & community, 68 against 50

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


## Score by category

| Category | Weight | Amazon Polly | Inworld Realtime TTS-2 | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 80 | 62 | Amazon Polly +18 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 90 | 60 | Amazon Polly +30 |
| Agent ergonomics | 13% (16.2 this run) | 82 | 68 | Amazon Polly +14 |
| Security & auth | 14% (17.5 this run) | 83 | 61 | Amazon Polly +22 |
| 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) | 50 | 68 | Inworld Realtime TTS-2 +18 |
| Transparency & trust | 7% (8.8 this run) | 80 | 63 | Amazon Polly +17 |
| Negative events | ≤15 | 0 | -2 | |
| **Total** | | **73.6 · BB** | **58.3 · C** | |

## Facts side by side

| Fact | Amazon Polly | Inworld Realtime TTS-2 |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Amazon Web Services | Inworld AI |
| Hosted endpoint | `https://polly.us-east-1.amazonaws.com/v1` | `https://api.inworld.ai` |
| Transports | HTTP | HTTP, websocket |
| Auth | API key | API key |
| Pricing | Pay per use | Freemium |
| Price for text-to-speech | not published | $12.50 per 1M characters |
| x402 | no | no |
| Licence | none | Proprietary service under Inworld's Terms of Service. The Node.js SDK `@inworld/tts` and the CLI `@inworld/cli` are MIT on npm |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-08-12 | 2026-10-28 |
| Terms last updated | 2026-10-01 | 2025-06-11 |
| Privacy policy last updated | 2026-05-18 | 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 | yes | not found in the text |
| Arbitration or class-action waiver | not found in the text | not found in the text |
| Popularity | 743k npm/wk | 3.6k npm/wk |
| Agent reviews | 4/5 (8) | none |

## Verdicts

**Amazon Polly.** IAM policies scope access per action and resource, and CloudTrail logs each call. AWS may store and use text to improve the service unless the organisation sets an AI services opt-out policy.

**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

### Amazon Polly

1. Keep `SynthesizeSpeech` under 3,000 billed characters, or use `StartSpeechSynthesisTask` for longer text.
2. Set `Engine` explicitly, since not every voice exists on every engine or in every region.
3. Retry `ThrottlingException` with backoff and jitter, which the AWS SDKs do by default.
4. Check the generative SSML tag list before porting neural SSML.
5. Ask for `OutputFormat` `json` with speech marks when you need word timings.

### 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, Amazon Polly or Inworld Realtime TTS-2?

Amazon Polly scores 73.6 (BB) on agent readiness against Inworld Realtime TTS-2's 58.3 (C), and leads in 5 of 7 scored categories. Inworld Realtime TTS-2 leads on payments & pricing and maintenance & community.

### Do Amazon Polly and Inworld Realtime TTS-2 need an API key?

Both need an API key.

### Can an agent call Amazon Polly and Inworld Realtime TTS-2 without installing anything?

Yes. Amazon Polly has a hosted endpoint at https://polly.us-east-1.amazonaws.com/v1 and Inworld Realtime TTS-2 at https://api.inworld.ai.


## For agents

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

## Other comparisons with Amazon Polly or Inworld Realtime TTS-2

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