Why isn’t my theme processing SASS?

It’s my understanding that WordPress now processes SASS files but for some reason mine don’t work.

I’m trying to call it using wp_enqueue_style directly in header.php via the head tag:

<?php wp_enqueue_style('stylesheet', get_template_directory_uri() . '/style.css', $ver = false, $media="screen") ?>

Instead, the file gets called as a normal CSS doc.

I attempted to rename style.css to style.scss but then the file doesn’t load at all, so I guess the sass pre-processor just isn’t firing.

@nipponese is right. WordPress doesn’t process Sass for themes. That was just for core files on wordpress.org.