Microsoft has released the Windows 10 Insider Preview Build 177353 (Redstone 5) in the Fast Ring. Furthermore the Windows 10 Insider Preview Build 18214 (19H1) for the Skip Ahead branch was released.
Windows 10 Insider Build 17735
The Windows 10 Insider Preview Build 177353 belongs to the RS5_RELEASE-Fork, which should lead to Windows 10 V1809 (or v1810) in autumn 2018. The announcement has been made as usual within the Windows blog. There you will find a longer list of changes and bug fixes. Unfortunately there is also a long list of known problems in the blog post.
Windows 10 Insider Build 18214
The Windows 10 Insider Preview Build 18214 is only available for testers whose system is configured for the Skip Ahead branch. There the code name 19H1 applies, since this development branch is to lead to the spring upgrade in 2019. The announcement was also posted on the Windows blog. There you can inform yourself about the new features, changes and bug fixes as well as about known problems.