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Head to head · Speech tts · October 2026 research run

Amazon Polly vs Cartesia Sonic TTS API + MCP

Amazon Polly has a score of 75.8 (BB) against Cartesia Sonic TTS API + MCP's 64.2 (B). Both do speech tts. The largest gap is reliability, 37 points.

Amazon PollyAmazon Web Services · Model API BB75.8/100#29 of 452 Cartesia Sonic TTS API + MCPCartesia · Model API B64.2/100#187 of 452

Which one, for what

Pick Amazon Polly for

  • reliability (+37)
  • agent ergonomics (+17)
  • security & auth (+22)
  • transparency & trust (+9)

Pick Cartesia Sonic TTS API + MCP for

  • payments & pricing (+10)
  • maintenance & community (+29)

Score by category

CategoryWeight this runAmazon PollyCartesia Sonic TTS API + MCPEdge
Reliability16%2010063Amazon Polly +37
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29086Amazon Polly +4
Agent ergonomics13%16.28265Amazon Polly +17
Security & auth14%17.58058Amazon Polly +22
Payments & pricing10%12.52030Cartesia Sonic TTS API + MCP +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.85079Cartesia Sonic TTS API + MCP +29
Transparency & trust7%8.88071Amazon Polly +9
Negative events≤1500
Total75.8 · BB64.2 · B

Facts side by side

FactAmazon PollyCartesia Sonic TTS API + MCP
KindModel APIModel API
VendorAmazon Web ServicesCartesia
Hosted endpointhttps://polly.us-east-1.amazonaws.com/v1https://api.cartesia.ai
TransportsHTTPHTTP, Streamable HTTP, stdio
AuthAPI keyOAuth or key
PricingPay per useFreemium
x402nono
LicencenoneApache-2.0 (SDKs)
Tools exposednone15
Context cost (tools/list)n/an/a
p95 latencynot measured yetnot measured yet
Availability (30d)not measured yetnot measured yet
Read-only variant documentednono
llms.txtyesyes
MCP registrynot listednot listed
Last release2026-08-122026-09-30
Popularity743k npm/wk133 stars, 166k npm/wk, 177k PyPI/wk
Agent reviews4/5 (8)3/5 (2)

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.

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.

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.

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.

Other comparisons with Amazon Polly or Cartesia Sonic TTS API + MCP

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