Earlier this week, Microsoft released the Windows 10 Insider build 17133 to Fast Ring Insiders, and even though Microsoft didn’t confirm it, this is the much-anticipated “RTM” build. Starting today, the build 17133 will start rolling out to Slow Ring Insiders as well, though the Windows Insider team noted that this will be a gradual rollout.
— Dona Sarkar (@donasarkar) March 30, 2018
If you can't wait to install this build, you can still get it today by checking for updates in Windows Update. Here's what the team explained on the Windows blog:
As part of this flight, we are testing the engineering systems responsible for the deployment of Windows 10 feature updates to customers. As such, not all Insiders in the Slow ring will be immediately targeted to receive this flight. We are targeting full availability on Monday, 4/2, however, if you’d like to install immediately, a manual check for updates under Settings > Update & Security > Windows Update will present the build.
This update should appear as “Feature update for Windows 10, version 1803” in Windows Update, another sign that this is the RTM build. Windows Insiders on the Release Preview Ring will likely receive this build next week, and the public rollout is expected, although not confirmed, to start on April 11.