Find out if Wordpress multisite uses subdirectory or subdomain for new blogs

Well, we have the very constant defined in wp-config.php:

if ( defined( 'SUBDOMAIN_INSTALL' ) ) {    if( SUBDOMAIN_INSTALL )        echo '<h2>Is: SUBDOMAIN</h2>';    else        echo '<h2>Is: SUBDIRECTORY</h2>';}

You can use wp_get_sites() to get information about your blogs. It will return an array containing information about all existing blogs.

Example result from the documentation:

Array(    [0] => Array(        [blog_id] => 1        [site_id] => 1        [domain] => example.com        [path] => /        [registered] => 2013-11-08 17:56:46        [last_updated] => 2013-11-08 18:57:19        [public] => 1        [archived] => 0        [mature] => 0        [spam] => 0        [deleted] => 0        [lang_id] => 0    )    [1] => Array(        [blog_id] => 2        [site_id] => 1        [domain] => example.com        [path] => /examplesubsite/        [registered] => 2013-11-08 18:07:22        [last_updated] => 2013-11-08 18:13:40        [public] => 1        [archived] => 0        [mature] => 0        [spam] => 0        [deleted] => 0        [lang_id] => 0    ))

[0] will be your main blog, so I'd ignore this. But by checking the first blog after that you should be able to get the information.

$info = wp_get_sites();if ($info[1]['path'] == "/") {    // the installation uses subdomains}else {    // the installation uses subdirectorys}

Of course this only works when there is at least one additional blog created, but I couldn't find any other option to check for.