As you may already know, the next major update to Windows 10, code named "Redstone 3", recently got its official name. Microsoft revealed that it will be called "Fall Creators Update". Now, it appears that Microsoft has referenced the version number for the Windows 10 Fall Creators Update in related documentation.
In a blog post which describes the Policy device description framework (DDF) file, the upcoming version is referenced as "Windows 10 version 1709". The reference is next to already released Windows 10 versions like 1703 and 1607.
This is quite expected. Microsoft uses the following numbering system:
- The first two digits, e.g. 17 - are for the year.
- The next two digits, e.g. 09 - are for the month.
Windows 10 Fall Creators Update is expected to be released in September 2017, so that's why it is named version 1709.
However, in case of Windows 10 Creators Update version 1703, which was expected in March 2017, there was an exception. While the operating system version indicates March 2017, it was only made public in April 2017. Despite the delay, the version number hasn't been changed.