It's been nearly a month since we saw a new Windows 10 Redstone 5 build in the Slow ring, but today, Microsoft offered build 17738.1000. It's only the third Redstone 5 build in the Slow ring so far, which is a bit odd considering that Fast ring builds are now rolling out at a pace of two per week. Usually, the Slow ring starts getting new builds at a faster pace than its normal one per month at this point.
You won't be getting a lot of new features, as development of the feature update has started to wind down. Microsoft is now focusing on fixes and refinements ahead of the RTM. Here are the builds that you missed, as Microsoft doesn't provide Slow ring changelogs:
Hopefully, Microsoft will also release an ISO for this build, as some Insiders do prefer a clean install. Being that there have only been two previous Slow ring builds from this branch and one wasn't eligible for ISOs, there's actually only been one Redstone 5 ever offered by Microsoft. In fact, the company usually offers the most recent two ISOs for download, but it can't even do that since the second most recent one is expired.
Windows 10 version 1809 will likely RTM next month, followed by a public release in October. Between now and then, we should see more frequent builds in the Slow ring.