Manual:$wgUseInstantCommons

Usage
Add the following to your  to enable InstantCommons:

Details
Setting this configuration parameter to  enables ic>Special:MyLanguage/InstantCommons|InstantCommons, which allows to automatically use in the local wiki images hosted in c>commons:|Wikimedia Commons.

This configuration parameter's setting is a shorthand for the following setting to  :

Note
Enabling this configuration parameter does not avoid any usage of disk space on the server running the local wiki.

Until MediaWiki 1.26, this setting did indeed generate thumbs on the local disk for caching purposes.

In case the dimensions of the original file on Wikimedia Commons are exceeded when embedding the file on a page in the local wiki, the file will in its original size be put onto the local disk.

Since MediaWiki 1.27 (251556),   hotlinks images from Commons by default instead of downloading originals and thumbnailing them locally.

This allows wikis to save on CPU and bandwidth while reducing time to first byte for pages, even without a thumbnail handler. This can make your wiki seem much faster

For example, if you have 100 InstantCommons images on a page, your wiki will make 400 API requests to the Commons API at page load time and the first byte of the page won't be returned for about 30 seconds. This can be somewhat improved by disabling $wgResponsiveImages

You may prefer to override the default   by creating your own   entry, or maybe not use foreign file repositories at all and instead copy images from Commons to your own wiki using  . Do note that counterintuitively,  is fastest if set to 0. Another aspect that has a major affect on performance is how long metadata is cached. Unfortunately this is currently not configurable and hard coded to 3600 seconds (1 hour) which is rather short

See the documentation of configuration parameter  for tweaks.