Reasoning · backend

Use o3 Mini with Express.js

Updated 2026-05-21 · By XALEN

How to use o3 Mini (Reasoning, ~200B) with Express.js. Install, authenticate, and make your first API call in minutes. Working code example included.

Model
o3 Mini
~200B · 200K context · $0.04 input
Framework
Express.js
backend · npm install xalen-sdk express

1. Install

npm install xalen-sdk express

2. Code

const express = require('express');
const XALEN = require('xalen-sdk');

const app = express();
app.use(express.json());
const client = new XALEN({ apiKey: 'xln_test_YOUR_KEY' });

app.post('/chat', async (req, res) => {
  const response = await client.chat.completions.create({
    model: 'o3-mini',
    messages: req.body.messages
  });
  res.json({ reply: response.choices[0].message.content });
});

app.listen(3000);

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Last updated: 2026-05-21