Add Universal endpoint

Author: kodster28

src/content/docs/ai-gateway/chat-completion.mdx

@@ -64,7 +64,34 @@ curl -X POST https://gateway.ai.cloudflare.com/v1/{account_id}/{gateway_id}/comp
 
 ### Universal provider
 
-TBD
+You can also use this pattern with a [Universal Endpoint](/ai-gateway/universal/).
+
+```ts title="index.ts"
+export interface Env {
+	AI: Ai;
+}
+
+export default {
+	async fetch(request: Request, env: Env) {
+		return env.AI.gateway("default").run({
+			provider: "compat",
+			endpoint: "chat/completions",
+			headers: {
+				authorization: "Bearer ",
+			},
+			query: {
+				model: "google-ai-studio/gemini-2.0-flash",
+				messages: [
+					{
+						role: "user",
+						content: "What is Cloudflare?",
+					},
+				],
+			},
+		});
+	},
+};
+```
 
 ## Supported Providers