https://www.bleepingcomputer.com/news/microsoft/windows-10-build-17751-released-to-insiders-with-build-watermark-removed/

Today, Microsoft is rolling out Windows 10 Build 17751 for Windows Insiders in the Fast Ring and it comes with a bunch of bug fixes. There are not too many changes as this development branch is in the last stages of the development process.

With the official name of Redstone 5 now being confirmed as the Windows 10 October 2018 Update, Microsoft is expected to sign off the RTM build for Windows 10 Redstone 5 next month. Due to this, the Windows 10 preview build 17751 is specifically focused on addressing bugs.