Gemini 3.8 Flash Is the Most Robust TTS Model on Our Board
Google's new Gemini 3.8 TTS models both land in the top naturalness group on our English board. Flash reads numbers more reliably than any model we have measured. Flash-Lite is twice as fast, and reads some debts as credits.
Google released Gemini 3.8 Flash TTS and 3.8 Flash-Lite TTS today. We ran both through the same three tests as every model on our TTS board: how natural it sounds, whether it reads numbers right, and how fast the first audio arrives.
Both land in the top naturalness group. Flash reads numbers better than anything we have measured.
| Model | Naturalness | Reads numbers right | First audio, US East | Per 1M characters |
|---|---|---|---|---|
| 3.1 Flash (previous) | 1591 | 0.68 | 851 ms | $33 |
| 3.8 Flash | 1642 | 0.95 | 1,013 ms | $15 |
| 3.8 Flash-Lite | 1639 | 0.68 | 481 ms | $10 |
Hear it
The same sentence on each.
3.1 Flash
3.8 Flash
3.8 Flash-Lite
Published copies are volume-matched; the models got the original text.
Flash keeps the minus sign
Our number-reading test sends 125 sentences with money, dates, times and codes, three draws each, and has several transcribers vote on what was said.
3.8 Flash scored 0.95, the highest we have measured. It kept every minus sign in the battery, and “-$12.50” and “-$1,204.50” came back negative in 40 of 40 extra draws. Its only misses were dates like “11/30/2024” read without the month.
3.8 Flash-Lite drops it. “The balance is -$12.50” came back as “twelve dollars and fifty cents” on four of seven draws. On a support call, that reads a debt as a credit.
3.1 ran in the same batch as a control and reproduced its published 0.68 exactly, including the refund it reads without the minus.
Speed and price
Flash-Lite is the fastest Gemini voice we have timed, at 481 ms to first audio. Flash is a little slower than 3.1. Both cost under half of 3.1 per character at launch pricing, which doubles on 1 January.
What to do
Use Flash when your agent reads amounts, balances or dates. Use Flash-Lite when speed and cost come first, and read its money back before you trust it.