Google: Gemini 3.8 Flash TTS vs HeyGen: HeyGen Voice Turbo
A side-by-side comparison of Google: Gemini 3.8 Flash TTS ($1.75 / 1M characters) and HeyGen: HeyGen Voice Turbo ($14.00 / 1M characters) using current USD prices and capabilities from the api14 catalog. Both run through the same OpenAI-compatible API.
Specifications
| Google: Gemini 3.8 Flash TTS | HeyGen: HeyGen Voice Turbo | |
|---|---|---|
| Provider | HeyGen | |
| Characters | $1.75 / 1M characters | $14.00 / 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 | Sep 23, 2026 | Oct 26, 2026 |
Key differences
- Google: Gemini 3.8 Flash TTS is 88% cheaper on input tokens.
In depth
Google: Gemini 3.8 Flash TTS is a speech model from Google, released on 23 September 2026. HeyGen: HeyGen Voice Turbo is a speech model from HeyGen, released on 26 October 2026. Both sit in the same category on api14, so you are comparing two text to speech systems rather than a speech model against a chat or vision model. If you already use other Google models through api14, the Gemini entry keeps your provider mix consistent, while HeyGen comes from a company known for its avatar and voice tooling.
On the technical facts listed, the two models look very similar. Both accept text as input and return speech as output, and neither exposes any supported parameters, so you cannot tune sampling behaviour, voice selection or speed through the request body on either one. Gemini 3.8 Flash TTS lists a context length of 32768 tokens. HeyGen Voice Turbo has no context length listed, so there is no documented figure to compare against, and the qualitative notes mark bigger context as not meaningfully different or unknown. The same applies to tool use, structured output and reasoning: none of those are listed as exclusive to either model. The one clear difference is price on input, where Gemini 3.8 Flash TTS is the cheaper side. Output pricing is marked as about the same, so the cost gap, if any, sits on what you send rather than what you get back.
For most tasks, the choice comes down to how much text you feed in per request. If you are synthesising long passages, such as narrating an article, reading out a document or generating audio for a large batch of copy, the cheaper input side and the documented context window make Gemini 3.8 Flash TTS the more predictable option. If your workload is short utterances, interface prompts, notifications or conversational lines, the input cost difference matters far less and either model will do the job. Because neither model exposes supported parameters, do not plan on controlling voice identity or prosody through the API on either side; treat both as fixed text in, speech out endpoints and handle variation elsewhere in your pipeline.
Calling either model through api14 works the same way, because the gateway is OpenAI compatible. You point your client at the api14 base URL, send a request to the chat completions endpoint with your API key, and set the model field to the id you want. To use Google's model, set the model to "google/gemini-3.8-flash-tts". To use HeyGen's, set it to "heygen/heygen-voice-1-turbo". Everything else in the request can stay identical: same authentication header, same message structure with your text as the user content, same response handling for the returned audio. Switching between the two is a one line change, so you can route different jobs to different models without maintaining two integrations.
There is no strong case in the facts for picking HeyGen Voice Turbo over Gemini 3.8 Flash TTS on capability grounds, since the modalities, parameters and qualitative flags are otherwise the same or unknown. The realistic reason to choose it is provider preference: if your team already works with HeyGen for voice or avatar production, keeping that model in the same account may simplify your workflow. Otherwise, with cheaper input pricing and a documented context length, Gemini 3.8 Flash TTS is the safer default, and you can still call HeyGen through the same api14 endpoint whenever you want to compare output.
Switch with one string
Both models use the same endpoint and request shape. Change the model value from "google/gemini-3.8-flash-tts" to "heygen/heygen-voice-1-turbo" 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": "heygen/heygen-voice-1-turbo",
"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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