While some are quibbling that Microsoft is going to be a month late with the Fall Creators Update release, I don't see things that way -- despite the fact Microsoft officials said this year that the company is aiming to deliver two feature updates per year, around March and September, to Windows 10 client and Server, going forward.
Microsoft still has yet to deem the Fall Creators Update as being feature-complete (or, as many of us still prefer to call it, RTM), but does plan to do so in September, hence its 1709 nomenclature. Microsoft also will designate a September build of Windows Server 2016's first feature update (1709) as its "launch" candidate, as the company plans to announce at its Ignite conference in late September. As "launch" and "release" don't always coincide with Microsoft products, Server 1709 also will likely begin rolling out to users in October.
Once Microsoft does decide Windows 10 Fall Creators Update is stable enough to ship, it will continue to update features and fix bugs in it. That means when users download the Fall Creators Update, they likely will also be downloading updates for it right off the bat, as well as in subsequent weeks and months.
Microsoft also will be releasing another new Windows 10 edition, known as Windows 10 Pro for Workstations, simultaneously with the release of the Fall Creators Update. No upgrade pricing information is available so far, but I've heard there will be an upgrade path and fee from Windows 10 Home and/or Pro to Workstation.