Microsoft today released Windows 10 Insider Preview build 17133 to the Fast ring, and as you'd expect, there are no new features. In fact, according to recent rumors, this is actually the RTM build for the upcoming spring update, which is codenamed Redstone 4. That means that this is the build that will ship on new PCs, and the one that non-Insiders will get when they upgrade existing devices.
As usual, Microsoft won't actually confirm this, saying that it's "in the final phase of checking in final code to prepare for the final release." This is interesting language that doesn't like to use the term RTM anymore because Windows 10 is never 'done'. In fact, Microsoft generally has trouble admitting that there's even any significance to being aware of which build will roll out to non-Insiders.
Although there aren't any new features today as Redstone 4 development wraps up, there are a few fixes and improvements:
We fixed an issue resulting in certain devices with BitLocker enabled unexpectedly booting into BitLocker recovery in recent flights.
We fixed an issue resulting in not being able to change the display resolution when there were 4 or more monitors connected, due to the confirmation prompt hanging when you selected “Keep changes”.
We fixed an issue where clicking suggested search terms when typing in the Microsoft Edge URL bar didn’t do anything.
There are no known issues in Windows 10 build 17133.
We'll know for sure that this is the RTM build when the company promotes it to the Release Preview ring, which is reserved for builds that will roll out to the general public. Until then, don't expect any help from Microsoft on this front.
There's also still a lot that we don't know about the Redstone 4 update, despite it essentially being ready to go. Signs point to it being called the Windows 10 Spring Creators Update, but that's not official yet. There's also been no official word as to when non-Insiders will have it made available to them.