WordPress 4.9.8 is a maintenance release which addresses 46 bug fixes.
With this update – you will also see the option to “try” the new block editor Gutenberg before it gets released with WordPress 5.0.
You can read more by looking at the release notes: https://codex.wordpress.org/Version_4.9.8
If you have not done so already – download the update or simply use your existing installation of WordPress to update your site. Either way – this is an excellent time to make a backup copy of your site(s) before upgrading.