As explained in T244204, the mobile applications (both Android and iOS, as far as I can tell) make a significant amount of requests to the MediaWiki API to fetch siteinfo.

Given they use urls like:

https://en.wikipedia.org/w/api.php?format=json&formatversion=2&errorformat=plaintext&action=query&meta=siteinfo

they get a response that is not cacheable by our caching infrastructure. This means that every time that an application needs to fetch those information, the request has to make it back all the way to the main datacenters, which is a cost both for the user[1] and for us, in terms of computational resources.

As explained in T244204#5877009, if you add &smaxage=N&maxage=N to the url, your result will be cached at the edge datacenters for N seconds.

Both applications should switch to using a cacheable url at the very least for the siteinfo requests.

[1] To quantify the advantage for users: a small benchmark from my mobile connection (a good 4G network in Europe) the mean time to fetch this information is 440 ms using the current url, while it drops to 314 ms if we use a cacheable url.