Today, Microsoft released the first Windows 10 Insider Preview from the Iron development branch, finally moving away from the meaningless mn_release branch. It doesn't contain any crazy new features, but there are a few new things for the Windows Subsystem for Linux.
Interestingly, the company also released some new ISOs, so if you want to do a clean installation, you can do that. As usual, your selection includes Windows 10, Windows 10 Enterprise, and Windows 10 Home China.
Microsoft usually doesn't publish ISO images this early in a development cycle. In fact, this is evident by the download options that the company offers for the Slow and Release Preview rings. The Slow ring is offered build 19041, the RTM build for 20H1, even though it started testing 20H2 yesterday. Moreover, the option for the Release Preview ring is offering a download for build 18363, the RTM build for 19H2, even though that ring has offered 20H1 since April.
If you want to download the new ISO images, you can find them here. Other than Windows Server, there aren't any other downloads available, such as a new SDK, ADK, WDK, HLK, or Desktop App Converter Base Image.