Remove custom post type slug from permalinks in WordPress

remove-custom-post-type-slug-from-permalinks.php

<?php

/**
 * Remove the slug from published post permalinks. Only affect our custom post type, though.
 */
function gp_remove_cpt_slug( $post_link, $post ) {

    if ( 'race' === $post->post_type && 'publish' === $post->post_status ) {
        $post_link = str_replace( '/' . $post->post_type . '/', '/', $post_link );
    }

    return $post_link;
}
add_filter( 'post_type_link', 'gp_remove_cpt_slug', 10, 2 );