> ## Documentation Index
> Fetch the complete documentation index at: https://docs.costa.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Build a Cosmic Router

<div class="tw-reset costatw:my-4 costatw:px-4 costatw:py-2 costatw:rounded-lg costatw:text-sm costatw:bg-zinc-100 costatw:text-zinc-600 costatw:dark:bg-zinc-800/50 costatw:dark:text-zinc-400">
  Routers only work on traffic flowing through Costa. If you haven't connected yet, [start there](/get-started/claude-code).
</div>

Cosmic Routers let you send requests to multiple models and providers. You can use them to extend your subscriptions by adding a second model.

Let's build one called `daily-driver` — 75% Opus on your Claude Max, 25% Kimi-K2.6 via OpenRouter.

<Note>Did you know, mixing models like this can increase overall performance? [Learn more](https://arxiv.org/pdf/2508.12631)</Note>

<Steps>
  <Step title="Add a second provider">
    Kimi-K2.6 is on OpenRouter, so let's add it.

    You'll need an OpenRouter API key. If you don't have one, [grab one from openrouter.ai](https://openrouter.ai/keys) — it takes a minute.

    1. Go to [**AI Providers**](https://ai.costa.app/admin/ai_providers) and click **Add provider**.
    2. Pick **OpenRouter** and paste your API key.
    3. On the OpenRouter row, click **Edit models** and add `kimi-k2.6` to the enabled list.
  </Step>

  <Step title="Build the router">
    1. Go to [**Models**](https://ai.costa.app/admin/code/models) and click **Add a router**.
    2. Name it `daily-driver`.
    3. Add two models with a 75/25 split:
       * **75%** → `claude-opus-4.7` (your Claude Max subscription)
       * **25%** → `kimi-k2.6` (via OpenRouter)
    4. Save.

    Your router is now available as `costa/daily-driver`.
  </Step>

  <Step title="Point your tool at it">
    <Tabs>
      <Tab title="Claude Code">
        In Claude Code, run:

        ```
        /model daily-driver
        ```
      </Tab>

      <Tab title="Codex">
        Not yet documented — see [Codex setup](/get-started/codex) for the model-config step.
      </Tab>

      <Tab title="opencode">
        Not yet documented — see [opencode setup](/get-started/opencode) for the model-config step.
      </Tab>
    </Tabs>
  </Step>

  <Step title="See it route">
    Send a few prompts. In your [session logs](https://ai.costa.app/code/sessions), click the latest session — every request shows the model your router picked, and you can watch the 75/25 split hold across the session.
  </Step>
</Steps>

That's a Cosmic Router. The subscription you already pay for. The open-weight models you heard about. Working together.

You're connected. You're trimming. You're routing. That's Costa.

Now go use it. The more traffic you send through, the more Costa learns about your work — and the more it can tell you back. We'll show you that next. But first: go build something.