It is expected to be 2 GB smaller than a standard Windows 10 Pro x64 installation.
Microsoft has detected a problem with using Windows 10 on low memory devices. The problem is that after downloading updates, there is not enough disk space left to install them without using an external drive. One answer is to get device manufacturers to deliver more memory, and the other is to reduce the size of Windows 1
As Windows Central reports, there is a new version of Windows 10 under development called internally Windows 10 Lean. It's aimed directly at devices with an internal storage capacity of only 16 GB, including a range of tablets and the HDMI port compute sticks we've seen in recent years.
Welcome to Windows 10 Lean / CloudE / S (once again?)
This new edition started with the Skip Ahead Build of the Week (17650)
It seems to be greatly reduced, an x64 clean Installation is about 2 GB smaller than Pro
Your edition id is 0xB7 What was missing in SDK headers pic.twitter.com/2Sn3SVXeZB
– Lucan (@tfwboredom) April 20, 2018  The first sign of Windows 10 Lean appeared in a Redstone 5 preview build and tweeted by Lucan . The goal seems to be 2GB smaller than a clean install of Windows 10 Pro x64.
Microsoft wants to achieve this by restricting functions and not compatibility. For example, while legacy apps continue to work, Lean users lose access to Internet Explorer and Registry Editor. Imagine an app or feature that a user is unlikely to use on such low-end devices, and it's probably not available in the Lean build.
For a less feature-rich version of Windows 10 to work, Microsoft also needs to tweak how Windows Update works. This is because the operating system still requires updates, but Microsoft does not want Lean to download content that can not be used because its functionality is not available.
It is unclear when we get the option Windows 10 Lean. My suspicion is that it is only offered as a preinstalled operating system on very low-end hardware. In fact, in the end, it might encourage some manufacturers to ship devices with only 16GB of storage.