The routing layer equates to the number of regions contained within the Smart CDN. On every single one of those regions, we are able to cache your content using an LRU mechanism.
Whether you need to apply manual adjustments to your code in order for the responses to be cached depends on what kind of resources the Builds you defined are creating:
Caching Static Files
There are no manual adjustments needed for caching Static Files. We cache the responses for 31 days on all the regions within the Smart CDN. By default we return a Cache-Control header containing public, max-age=0, must-revalidate that specifies the client should not cache. This can be overridden with the routes property in your now.json file.
Caching Lambda Responses
In order to cache the response of a Lambda that was created by any of your Builds, you need to make sure to manually set the Cache-Control header and assign it a value that contains the s-maxage parameter (the equivalent of max-age, but for shared caches).
You can read more about the suggested way to define this property here.