add_action( 'genesis_before_loop', 'sk_latest_post', 15 );
function sk_latest_post() {

	// WP_Query arguments
	$args = array (
		'cat'            => get_query_var( 'cat' ),
		'no_found_rows'  => true,
		'posts_per_page' => '1',
	);

	remove_action( 'genesis_entry_header', 'genesis_post_info', 12 );
	add_action( 'genesis_entry_header', 'genesis_post_info', 7 );

	genesis_custom_loop( $args );

	remove_action( 'genesis_entry_header', 'genesis_post_info', 7 );
	add_action( 'genesis_entry_header', 'genesis_post_info', 12 );
}