Frontier · backend

Use GPT-4o with FastAPI

Updated 2026-05-21 · By XALEN

How to use GPT-4o (Frontier, ~1T) with FastAPI. Install, authenticate, and make your first API call in minutes. Working code example included.

Model

GPT-4o

~1T · 128K context · $0.05 input

Framework

FastAPI

backend · pip install xalen fastapi uvicorn

1. Install

pip install xalen fastapi uvicorn

2. Code

from fastapi import FastAPI
from pydantic import BaseModel
from xalen import XALEN

app = FastAPI()
client = XALEN(api_key="xln_test_YOUR_KEY")

class ChatRequest(BaseModel):
    messages: list

@app.post("/chat")
async def chat(req: ChatRequest):
    response = client.chat.completions.create(
        model="gpt-4o",
        messages=[m.dict() for m in req.messages]
    )
    return {"reply": response.choices[0].message.content}

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Last updated: 2026-05-21