Cartesia plan price per 1,000 characters vs Sume TTS on Sonic

The comparison

Per 1,000 characters, Cartesia's Pro plan works out to $0.05, Startup to about $0.0392 and Scale to about $0.0374, while Sume's pay-as-you-go TTS is $0.0475. Sume is cheaper than Pro and cheaper than the other two plans if you use less than the plan's credits.

Cartesia counts one credit per character, and the Sonic models are the same engine family that Sume's POST /v1/tts-router/generate calls (sonic-3.6, sonic-3.5, sonic-3, sonic-latest, sonic-preview).

Plan arithmetic

The plan figures come from Cartesia's pricing page. Divide the price by the credits, then by 1,000. Free is 20,000 credits and costs nothing.

Where each wins

Read the last column as a break-even. If you use fewer characters in a month than that number, Sume costs less than the plan, because you pay only for characters you send. If you use more, the plan is cheaper per character. For Scale that crossover is about 6.3 million characters, and for Startup about 1.03 million.

That ignores unused credits and any overage rules, so read Cartesia's terms before you rely on the break-even. It also ignores everything that is not price: Sume gives you one jobs API with idempotency keys and webhooks shared with its other tools, plus pronunciation dictionaries and sentence segments from the same request.

Picking a model id

Send model on the router; it is required, and the rejected-on-1.0 rule means sume/tts-1.0 takes no model at all. Cartesia's model docs (read 2026-10-04) describe Sonic 3.6 with 44 languages. Use sonic-latest only if you accept silent upgrades, and pin sonic-3.6 for a series that must sound the same.

• GET /v1/tts-router/models lists what your key can call.
• Set language for every non-English transcript.
• Characters include spaces and punctuation on both sides.
• Check Cartesia's current terms before you commit to a plan.

Turning minutes into characters

Cartesia's pricing page says one minute of audio is about 750 to 800 credits, and a credit is a character. So a 10-minute narration is roughly 7,500 to 8,000 characters. On Sume that is 7.5 x $0.0475 = $0.356 to 8 x $0.0475 = $0.38 per 10 minutes, and a plan only pays off when you generate hours of audio each month.

Sume's own page on how long a TTS minute is explains the same conversion from the 1,200-second job cap. Count your real script rather than guessing: send the exact text you will bill, since spaces and punctuation are characters on both services. A script with long numbers, URLs or stage directions is longer than it looks, so trim those before you compare plans, and keep one spreadsheet row per episode so the monthly total is a sum you can check against the invoice.