Windows 10 has moved away from a "Service Pack" model to a "yearly major feature update" model.
In practice, not a whole lot has changed, though! You'll be pleased to know that Microsoft makes ISO files available for download for the Windows 10 Anniversary Edition Update, which is a "Service Pack" in all but the name (its actual functionality is effectively identical to what they used to call a "Service Pack").
If you install Windows from an Anniversary Edition ISO (i.e., "Build 1607"), you'll have to do significantly less patching post-install than if you install from the "Windows 10 RTM" (Release To Manufacturing - the original Windows 10 build) ISO.
That said, there is currently no easy way that I know of to install to an end-user machine from a Windows ISO (with a graphical installer, etc.) that will leave you fully updated on first boot. This is possible using something called Slipstreaming where you basically build your own custom ISO that consists of the latest Windows Build (i.e. 1607) plus the latest Updates (which are so-called "slipstreamed into" the ISO file upon build). This is for advanced users as it's not especially easy or user-friendly to do it, and it's only worth your time to do so if you intend to reinstall very frequently or install Windows on many, many machines (5 or more).
The slipstreaming process, briefly, involves:
- Download and run WHDownloader
- Grab all the updates
- Grab an official ISO file of Windows 10 from Microsoft; e.g. you can find some links here (the direct links to Microsoft or its Content Delivery Network are legal ways to download Windows media; Microsoft no longer places tight control on the download of Windows installation media.)
- Use a slipstreaming tool, such as NTLite, to first open your Windows 10 ISO (the original, which you downloaded from Microsoft), and then slipstream all your updates into it.
The Winbuzzer article I linked to above contains some detailed instructions with screenshots, but I captured the general flow of it here for posterity's sake (I didn't want to take their images due to copyright).