The Geforce 389.86 Hotfix driver is only available to Windows 10 users since only Windows 10 users were plagued by this problem and it includes all the features and updates from the recently released Geforce 398.82 WHQL driver.

According to the release notes, it fixes the issue where windowed G-Sync mode could stutter after applying the Windows 10 April 2018 update.

As always, you can find the new Geforce 398.86 Hotfix driver over at Nvidia's support page.