Gemini 3.8 Flash TTS vs Sume TTS: break-even is 47 characters

Google bills Gemini 3.8 Flash TTS by audio length: $0.00225 per 10 seconds through December 31, 2026. Sume bills TTS by characters: $0.0475 per 1,000. The two meet at about 47 characters of script per 10 seconds of audio ($0.00225 / $0.0000475 = 47.4). Real narration usually packs more characters than that into 10 seconds, which would put Google ahead, but that depends on your voice, language and pacing, so measure your own script.

The break-even line

Because one is priced per second and the other per character, the speech rate decides the winner. The table gives the cost of 10 seconds of audio at three script densities. The densities are hypothetical examples, not measurements of any voice.

Cost of 10 seconds of audio at three assumed densities.

The January 2027 change

Google's page lists the audio output rate as $9.00 per million tokens through December 31, 2026 and $18.00 starting January 1, 2027, so the per-10-second figure doubles to $0.0045. The break-even then moves to about 95 characters per 10 seconds ($0.0045 / $0.0000475 = 94.7). A script that is cheaper on Sume in 2027 is one that speaks fewer than about 95 characters per 10 seconds.

Gemini 3.8 Flash also has a batch tier at $4.50 per million audio tokens through 2026, about $0.001125 per 10 seconds, which moves the 2026 break-even down to roughly 24 characters.

Constraints on the Sume side

A single Sume TTS request is capped at 20,000 characters, which costs $0.95. The catalog lists sume/tts-1.0 and sume/tts-router at the same character rate. Sume's rate is easy to forecast from the script length alone, before any audio exists, which is the practical advantage of per-character billing.