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S2.1 Pro vs HeyGen Voice: API price, context & features · api14

Fish Audio: S2.1 Pro vs HeyGen: HeyGen Voice

A side-by-side comparison of Fish Audio: S2.1 Pro ($52.50 / 1M characters) and HeyGen: HeyGen Voice ($52.50 / 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	HeyGen: HeyGen Voice
Provider	Fish Audio	HeyGen
Characters	$52.50 / 1M characters	$52.50 / 1M characters
Context window	-	-
Max output	-	-
Input	text	text
Output	speech	speech
Tool calling
Structured output
Reasoning control
Added	Jul 29, 2026	Oct 13, 2026

Key differences

Both have about the same input price.

In depth

Fish Audio: S2.1 Pro is a speech model from Fish Audio, and HeyGen: HeyGen Voice is a speech model from HeyGen. Both sit in the same category on api14, both take text as input, and both return speech as output. Neither exposes a context length in the catalog data, and neither lists any supported parameters, so on paper they are close siblings: two text to speech endpoints sold through the same gateway, distinguished mainly by the vendor behind them and by the release timing recorded for each.

The capability comparison is deliberately thin, because the data does not support much more. Input modalities match (text only), output modalities match (speech only), and there is no context window figure to compare for either model. The one qualitative signal available is cost on the input side, and that comes back as a tie, meaning the two are about the same price for input. Output pricing is not marked as different either, so there is no cost argument that clearly favours one over the other. Nothing in the data says one model supports tool calling, structured output or reasoning that the other lacks. If you are choosing between them, you are choosing between two vendors' voices, not between two feature sets.

Practically, that means the decision should be driven by the voice you want and by how the vendor's output sounds on your material, not by a spec sheet. If your product already uses Fish Audio voices elsewhere, or your team has tuned prompts and pacing around Fish Audio output, S2.1 Pro keeps that consistent. If you are building around HeyGen, for example because your pipeline already produces HeyGen avatars or video and you want the spoken track to come from the same vendor, HeyGen Voice is the natural fit. Because input cost is about the same, you can run both on a sample of your real scripts and pick on listening quality, latency in your own environment, and how each handles the languages and speaking styles your users actually need.

Calling either one through api14 works the same way, because the gateway speaks the OpenAI-compatible chat completions shape. You point your client at the api14 base URL, send your text as the user message, and set the model field. To use Fish Audio you set the model id to "fish-audio/s2.1-pro"; to use HeyGen you set it to "heygen/heygen-voice-1". Everything else in the request body stays as it is, and the response comes back with audio in the same structure, so switching vendors is a one line change and you can keep a single code path with the model id as configuration rather than branching logic.

There is no case in the supplied facts where one model is clearly the better pick on capability grounds, since the only qualitative difference recorded is a tie on input cost and the rest is unknown or not meaningfully different. So the honest guidance is to treat them as interchangeable from the API's point of view and let the voice itself decide. Keep the model id in config, test both against your real scripts, and switch if one sounds better for your use case.

Switch with one string

Both models use the same endpoint and request shape. Change the model value from "fish-audio/s2.1-pro" to "heygen/heygen-voice-1" and prompts, streaming and tools keep working.

Fish Audio: S2.1 Pro details & playground →HeyGen: HeyGen Voice details & playground →

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",
  "input": "Hello from api14! One API for every model.",
  "voice": "alloy",
  "response_format": "mp3"
});
await writeFile("speech.mp3", Buffer.from(await audio.arrayBuffer()));

Fish Audio: S2.1 Pro vs HeyGen: HeyGen Voice

Specifications

Key differences

In depth

Switch with one string

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