WebP is an image format developed by Google. The premium version of WP Fastest Cache optimizes the images as well as generates the webp image extension of the images.
Generating webp image does not mean that adding “.webp” extension at the end of the images. If the browser supports WebP images, the images are served a .webp image instead of jpg/png. The operation is done via htaccess so if the web-server is Nginx or Microsoft IIS, WebP does not work.