OpenAI-compatible APIs

Use GistUI with the Vercel AI Gateway, OpenRouter, Groq, Together, Ollama, vLLM and any other API that speaks OpenAI's Chat Completions format.

Most gateways and model servers accept OpenAI’s Chat Completions request and return its streaming format. For all of them the code is the same; only the URL, the key and the model id change.

api/answer.tsts

import { prompt } from "@gistui/catalog";
import { textDeltas, toReadable } from "@gistui/server";

const URL = "https://ai-gateway.vercel.sh/v1/chat/completions";
const KEY = process.env.AI_GATEWAY_API_KEY;
const MODEL = "openai/gpt-oss-120b";

export async function POST(req: Request) {
  const { messages } = await req.json();
  const res = await fetch(URL, {
    method: "POST",
    headers: { Authorization: `Bearer ${KEY}`, "Content-Type": "application/json" },
    body: JSON.stringify({
      model: MODEL,
      stream: true,
      messages: [{ role: "system", content: prompt().text }, ...messages],
    }),
  });
  if (!res.ok) return new Response(await res.text(), { status: res.status });
  return new Response(toReadable(textDeltas(res, "openai")));
}

Endpoints

Service	URL	Model id looks like
Vercel AI Gateway	`https://ai-gateway.vercel.sh/v1/chat/completions`	`openai/gpt-oss-120b`
OpenRouter	`https://openrouter.ai/api/v1/chat/completions`	`google/gemini-3.7-flash`
Groq	`https://api.groq.com/openai/v1/chat/completions`	`openai/gpt-oss-120b`
Together	`https://api.together.xyz/v1/chat/completions`	the provider’s model name
Ollama (local)	`http://localhost:11434/v1/chat/completions`	`qwen3:8b`
vLLM, LM Studio, llama.cpp	your server’s `/v1/chat/completions`	whatever you loaded

Model ids change often: check the service’s own list.

Local models

A local server needs no key. Small models follow the prompt less exactly; two things help.

A smaller prompt. Leave out the groups you do not need: prompt({ groups: ["Layout", "Content", "Data"] }).
Autofix. It is on by default in every renderer and repairs most slips in code. See Autofix and repair.

In a chat

The openai() adapter of @gistui/chat speaks to any of these through your endpoint:

import { createChat, openai } from "@gistui/chat";

const store = createChat({ adapter: openai({ model: "openai/gpt-oss-120b", url: "/api/chat" }) });