TeamWin Recovery Project has made its way to Samsung's Galaxy S8 and S8 Plus flagships, but only the international versions based on Samsung's own Exynos processors. The implementation of TWRP here requires flashing through Samsung's ODIN tool and requires enabling OEM Unlock in your phone's Developer Settings. There are, of course, a few caveats, but on the whole, early testers say that TWRP works fairly well, and the downsides should be easy to overcome for most users interested in things like rooting and flashing a custom ROM. All the files you need for the Galaxy S8 Plus can be found by following the source link below, courtesy of XDA Developers user "jesec," while user "mwilky" compiled the necessary files for the Galaxy S8 Plus.
Before proceeding, users should take heed that going through with this process will trip Samsung's KNOX protection which means that they will not be able to use Samsung Pay. While past phones have had KNOX re-enablers available, no such app has yet been made for the Galaxy S8 and Galaxy S8 Plus, so there's no reversing this process as of this writing. If you want to flash TWRP on your device despite the downsides, you'll first have to enable your phone's Developer Settings by tapping on the "Build number" option in your Settings menu, then check "OEM Unlock" on the following screen. After you've done that, simply grab the files for the correct version from the relevant thread on XDA Developers, boot your phone into Fastboot mode, and flash it through ODIN according to the instructions.
Despite the drawbacks, having TWRP available on your device does have its benefits, including being able to flash your root solution of choice. A screenshot from jesec shows Magisk manager working quite well on the Galaxy S8 Plus. Magisk has the bonus of Magisk Hide, which allows you to use apps that search for root, unlocked bootloaders, and other mods, meaning things like Android Pay and Pokemon GO can still work. A rooted device means that you can use an app like Titanium Backup to remove the Samsung apps that you don't want to use and even modify your hardware button mapping files to try and remap the Bixby button. Users can even wipe their system and flash custom ROMs for the Galaxy S8 and the Galaxy S8 Plus. Those who are okay with sacrificing a bit of security can also decrypt their device via TWRP for a bit of a speed boost, though the boost in question may be marginal at best.