Fish Audio: S2.1 Pro Free (free) vs Google: Gemini 3.8 Flash TTS
A side-by-side comparison of Fish Audio: S2.1 Pro Free (free) (Free) and Google: Gemini 3.8 Flash TTS ($1.75 / 1M characters) using current USD prices and capabilities from the api14 catalog. Both run through the same OpenAI-compatible API.
Specifications
| Fish Audio: S2.1 Pro Free (free) | Google: Gemini 3.8 Flash TTS | |
|---|---|---|
| Provider | Fish Audio | |
| Characters | - | $1.75 / 1M characters |
| Output | - | $31.50 / 1M tokens |
| Context window | - | 32,768 |
| Max output | - | 16,384 |
| Input | text | text |
| Output | speech | speech |
| Tool calling | ||
| Structured output | ||
| Reasoning control | ||
| Added | Jul 29, 2026 | Sep 23, 2026 |
In depth
Fish Audio: S2.1 Pro Free (free) is a text to speech model from Fish Audio, released on 2026-07-29. Google: Gemini 3.8 Flash TTS is a text to speech model from Google, released on 2026-09-23. Both sit in the speech category, so neither is a general purpose chat or reasoning model. You send text in and get audio out. That is the whole shape of the job for both of them.
On capabilities the two are closer than the branding suggests. Both accept text as the only input modality and both return speech as the only output modality. Neither lists any supported parameters, so you cannot tune sampling, voice, speed or format through the request body on either one. The one concrete difference in the data is context length. Gemini 3.8 Flash TTS lists 32768 tokens. Fish Audio S2.1 Pro Free lists no context length at all, which means it is unknown rather than zero. If your input text is long, a script, a chapter, a long article, that number matters, and only one of the two gives you a number to plan against. The qualitative comparison fields come back null across the board, so there is no stated edge on price, context or tool support to lean on. Treat them as functionally similar speech endpoints with one documented context figure between them.
For picking, start from the input length and the billing question. If you are synthesising short strings, UI prompts, notifications, a few sentences of narration, either model will do and the free tier on the Fish Audio side is worth testing first. If you are feeding in long documents and need to know whether the text will fit, Gemini 3.8 Flash TTS is the safer default because its 32768 token window is stated and you can measure against it. If you need a specific voice, emotion control or audio format, check the live price table and the model pages before committing, because neither model advertises tunable parameters here. Do not assume one is cheaper: the price fields are not given, so compare the live table yourself.
Calling either one through api14 is the same request. Both are OpenAI-compatible, so you point your client at the api14 base URL, send a normal chat completions style payload with your text, and read the audio back from the response. The only line that changes is the model id. Use "fish-audio/s2.1-pro-free:free" for the Fish Audio model and "google/gemini-3.8-flash-tts" for the Google model. Everything else, headers, auth, request shape, stays put. That makes switching cheap: you can route short jobs to one and long jobs to the other behind a single function that takes the model id as an argument.
There is one case where the Fish Audio model is still the better pick even with the context gap. Because it is free, it is the right choice for prototyping, for tests that run often, and for any workload where you are still deciding whether the feature is worth paying for. Once the text gets long enough that you cannot be sure it fits, move to Gemini 3.8 Flash TTS.
Switch with one string
Both models use the same endpoint and request shape. Change the model value from "fish-audio/s2.1-pro-free:free" to "google/gemini-3.8-flash-tts" and prompts, streaming and tools keep working.
import { writeFile } from "node:fs/promises";
import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://api14.com/api/v1",
apiKey: process.env.API14_API_KEY,
});
const audio = await client.audio.speech.create({
"model": "google/gemini-3.8-flash-tts",
"input": "Hello from api14! One API for every model.",
"voice": "alloy",
"response_format": "mp3"
});
await writeFile("speech.mp3", Buffer.from(await audio.arrayBuffer()));
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