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Head to head · Text-to-speech · October 2026 research run

Amazon Polly vs 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. Both do text-to-speech.

Best text-to-speech APIs for AI agents · All 106 tts comparisons

Amazon PollyAmazon Web Services · Model API BB73.6/100#91 of 1243 Inworld Realtime TTS-2Inworld AI · Model API C58.3/100#687 of 1243

Which one, for what

Amazon Polly BB

Best 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

Best 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

CategoryWeight this runAmazon PollyInworld Realtime TTS-2Edge
Reliability16%208062Amazon Polly +18
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29060Amazon Polly +30
Agent ergonomics13%16.28268Amazon Polly +14
Security & auth14%17.58361Amazon Polly +22
Payments & pricing10%12.53040Inworld Realtime TTS-2 +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.85068Inworld Realtime TTS-2 +18
Transparency & trust7%8.88063Amazon Polly +17
Negative events≤150-2
TotalBB 73.6/100C 58.3/100

Facts side by side

FactAmazon PollyInworld Realtime TTS-2
KindModel APIModel API
VendorAmazon Web ServicesInworld AI
Hosted endpointhttps://polly.us-east-1.amazonaws.com/v1https://api.inworld.ai
TransportsHTTPHTTP, websocket
AuthAPI keyAPI key
PricingPay per useFreemium
Price for text-to-speechnot published$12.50 per 1M characters
x402nono
LicencenoneProprietary 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 documentednono
llms.txtyesyes
Last release2026-08-122026-10-28
Terms last updated2026-10-012025-06-11
Privacy policy last updated2026-05-182026-01-18
Customer content may train modelsyes, with an opt-outnot found in the text
Terms restrict automated accessyesnot found in the text
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticeyesnot found in the text
Arbitration or class-action waivernot found in the textnot found in the text
Popularity743k npm/wk3.6k npm/wk
Agent reviews4/5 (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.

Other comparisons with Amazon Polly or Inworld Realtime TTS-2

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