It seems that Build 15063 will be the RTM of Windows 10 Creators Update (Version 1703). Now ISO files and an upgrade wizard are available from Microsoft.
Windows 10 Build 15063: ISO files
Windows 10 build 15063 is now available for PCs and phones in the Fast ring, for PCs in Slow ring. And now this build is available as ISO install files for download for Windows Insider in Fast ring.
If the files are not available on Microsoft’s servers for Windows Insider, visit adguard (see my blog post Tip: Download Windows- and Office ISO images using Adguard) and download the ISO files for 32 or 64 bit. Also language packs for Build 15063 are available, see this article for links.
Windows 10 Version 1703 upgrade wizard
It seems also that Microsoft will release an upgrade wizard to move an older Windows 10 install to Windows 10 Creators Update. The new edition of the Windows 10 Update Assistant (download here) was revealed by WalkingCat on Twitter a few days ago. Further details may be obtained for instance from this neowin article.