Microsoft has released the update KB4100347 for the latest build Windows 10 1803, which was released to the public on April 30, 2018.
Build 1803 has a lot of issues with Windows 10 and many are complaining about incompatibilities with certain hard drives, bluescreens, network devices and more.
It should be noted here that the Windows 10 April 2018 Update did not include the microcode update that protects against attacks targeting the Specter vulnerability, while Microsoft had released microcode updates to all previous versions of Windows 10. (Some successfully and some not)
This time Microsoft took two weeks to release the microcode update for build 1803 via update KB4100347 on May 15, 2018 (last night). The update is currently available through Windows Update and the Microsoft Update Catalog website. It is for Windows 10 build 1803 and Windows Server 2016 build 1803 (Server Core).
Devices configured to automatically download updates via Windows Update will automatically install the microcode update at some point, provided the system processor is supported.
You can see the list of supported processors in Microsoft support page. Processors Kaby Lake, Coffee Lake, Broadwell, SkyLake, Haswell, Bride Ivy and Sandy Bridge are included. Microsoft continues to update Windows code to support additional processors.
If you want you can download the update directly from Microsoft Update Catalog. It has a size of 1 Megabyte.