Microsoft has been extremely slow to release new ISO images for Windows 10 Redstone 5. The first one showed up on July 31 after the feature update had been in testing for months. Today, Microsoft released ISOs for Windows 10 build 17738.
The good news is that it comes only five days after the build was released to the Slow ring. The Insider team promised at the time that ISOs would be available, and it delivered this time. This is the second Redstone 5 ISO, and build 17738 was only the third build for the Slow ring.
Windows 10 build 17738 is all caught up on the new features that we've seen in the Fast ring, and you probably won't see any new features for the rest of Redstone 5 development. The feature update is Windows 10 version 1809, and Microsoft hasn't told us what the actual name of the update will be.
If you want to do a clean install of Windows 10 Insider Preview build 17738, you can download the new ISO images here.