Tiered TTS per-unit pricing vs Sume's flat $47.50 per million
Cartesia overage is $65, $45 or $38 per million credits by plan; Inworld TTS-2 runs $25 to $12.50. Sume sells TTS at one rate: $47.50 per million characters.
Two vendors price text-to-speech by plan tier: the more you commit, the less each character costs. Sume has one published rate, **$0.0475 per 1,000 characters ($47.50 per million)**. The flat rate is not the lowest in any tier-by-tier comparison, but it is predictable from the first character.
What the vendors publish
On Cartesia's pricing page, one credit is one character. Overage per million credits is $65 on Pro, $45 on Startup and $38 on Scale. The plans are $5 (100K credits), $49 (1.25M) and $299 (8M).
Inworld's TTS-2 is $25 per million characters on-demand, falling to $12.50 on Growth, and as low as $5 on Enterprise.
| Provider / plan | Per million characters |
|---|---|
| Cartesia Pro overage | $65 |
| Cartesia Startup overage | $45 |
| Cartesia Scale overage | $38 |
| Inworld TTS-2 On-Demand | $25 |
| Inworld TTS-2 Growth | $12.50 |
| Sume sume/tts-1.0 | $47.50 |
Where the Sume number comes from
The Sume rate is built on Cartesia at 1 credit per character and $38 per million credits, the Scale overage, times 1.25: $38 x 1.25 = $47.50. So Sume's TTS is the Scale-tier rate with the multiplier, available without a plan.
A maximum job is 20,000 characters, which is $0.95.
Which one is cheaper
For one million characters in a month: Cartesia Startup at $49 includes 1.25M credits, so it costs $49 flat. Sume is $47.50 for one million. Cartesia Pro costs $5 for the first 100K plus 900K at $65 per million, which is $63.50. Inworld On-Demand is $25.
A vendor plan beats Sume when your volume sits well inside its included credits. Sume wins on a low or lumpy volume when you do not want to hold a subscription for it.
What to check before choosing
Add the 5.5% platform fee to the Sume number when you budget. Compare against your actual monthly characters, not the sticker rate.
The case for a flat rate
A tiered plan makes the effective price depend on your month. A quiet month on Cartesia Pro means paying $5 for 100K credits you might not use, and a busy month pushes you into the $65 overage. Neither is wrong, but the cost per character moves.
A flat rate is easy to put in a quote. 20,000 characters is $0.95 at Sume's rate, before the 5.5% fee, every time.
Make your own comparison
Take your last three months of characters. For each vendor plan, compute the plan fee plus any overage. For Sume, multiply by $0.0475 per 1,000 and add the fee. Pick the lowest, and re-check when your volume changes. Vendor tiers also change, so reread their pages before you commit.
Sources
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