Next.js and Vercel AI SDK

import { streamText } from "ai";
import { openai } from "@ai-sdk/openai";

export async function POST(req: Request) {
  const { messages, userId } = await req.json();
  const latestInput = String(messages.at(-1)?.content || "");

  // 1. Pre-screen with Gated (<1ms edge check)
  try {
    const gateRes = await fetch("https://getgated.ai/v1/check", {
      method: "POST",
      headers: {
        Authorization: `Bearer ${process.env.M6L_GATE_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        user: userId || "anon",
        input: latestInput,
        messages: messages.length,
        feature: "nextjs_chat",
      }),
      signal: AbortSignal.timeout(400),
    });
    if (gateRes.ok) {
      const gate = await gateRes.json();
      if (!gate.allow) {
        return Response.json({ role: "assistant", content: gate.message }, { status: 200 });
      }
    }
  } catch {
    // Fail open on timeout
  }

  // 2. Safe to call OpenAI or Anthropic
  const result = streamText({
    model: openai("gpt-4o"),
    messages,
  });
  return result.toDataStreamResponse();
}