Microsoft has pushed an older build of Windows 10 October 2018 Update, codenamed RS5 (Redstone 5), which is still in development to Slow ring of Windows Insider program and released the ISO images for it. The build is Windows 10 v.1809 Build 17744.
As newer builds for Windows 10 October 2018 Update have been released, the build 17744 is unlikely to be the final RTM build that is going to be released to end user. But it’s currently the newest version of Windows 10 RS5 which Microsoft made available its ISO images for free download officially.
If you need the ISO images for Windows 10 Insider Preview Build 17744, head to Windows Insider Preview Downloads section of Windows Insider website. To access the downloads, you need to be a member of the Windows Insider program.
3 versions of Windows 10 Insider Preview Build 17744 are available, namely the general ISO consisting of these editions: Home, Pro, Education, and Home Single Language; Enterprise and Home China.
Update: Windows 10 October 2018 Update Build 17754