Their exploit, dubbed WeakSauce, gains root, and mounts a new xbin partition containing busybox as well as superuser. While the method was designed for the Verizon variant of the M8, the devs state that it should work for all variants. Although some are reporting that International variants are not playing nice with this method, that's about the worst that can happen—you may not be rooted, but you certainly won't brick your device.
We'll have a full guide for you guys shortly, but until then, check out the instructions below.
Making sure you have "Unknown sources" enabled in your Security settings, grab the file for WeakSauce (app mirror), unzip it, and run the app. After it does its thing, head to Google Play and install Chainfire's SuperSU.
Now simply reboot your device and you're rooted! Nice and easy.
Remember, this method re-roots the device on every boot (no permanent root until the M8 gets S-OFF), so give your device about 30 seconds on each boot for the exploit to do its thing.
Because your device doesn't maintain root permanence, using Xposed Framework is somewhat buggy at the moment. The only method of Installing Xposed is to rely on "soft reboots" within the app itself. Meaning, if you install Xposed, update the framework, or activate any modules, make sure to select "soft reboot" from the app's reboot menu.
As easy as this rooting method is, it's even easier to unroot. Simply uninstall WeakSauce, uninstall SuperSU, and reboot.
As the method and process are new, we'll probably be seeing quite a few updates from the devs. To update, simple uninstall the two apps just like you would to unroot, then reinstall them after rebooting.
Root checker image via whskytango/XDA