Connect Client

Product clients use User City. The common paths are client.ai.* for AIService and client.service(id).action(name).invoke() for custom services.

import { City } from "@downcity/city";

const client = new City({
  role: "user",
  federation_url: "https://base.example.com",
  city_id: "city_xxx",
  user_token: "ub_xxx",
});

const catalog = await client.ai.listModels();

const result = await client.ai.text({
  model: catalog.default(),
  prompt: "Write a welcome message for the product",
});

If you already know the target model, select it directly from the directory:

const body = await client.ai.stream({
  model: catalog.get("gpt-5.4"),
  prompt: "Stream a short paragraph",
});

ai.text() returns an AI SDK UIMessage. ai.stream() returns ReadableStream<UIMessageChunk> when the City-side stream handler returns an AI SDK UIMessage stream response.

One Federation can serve many client surfaces:

• https://app.example.com
• a Chrome extension
• a desktop tool
• a mobile app
• an internal operations tool

Those clients do not need to manage provider keys, model routing, or usage tracking on their own.