Windows 10 version 1803 comes one step closer to its public release today, as Microsoft seeded build 17133 to the Slow ring. It was originally released to the Fast ring three days ago, and is likely to be the RTM build for the upcoming feature update to the OS. This means that it's the same build that non-Insiders will receive when it rolls out to the public in a couple of weeks, and the one that will be installed on new PCs.
In fact, as you can see from the image above, it doesn't say that it's Windows 10 Insider Preview build 17133; instead, it shows up as Feature update to Windows 10, version 1803. This is the message that non-Insiders will see, as it's similar in format to the updates that arrived for the Windows 10 Fall Creators Update (version 1709) and earlier.
There aren't any new features since the last Slow ring build, which was 17127. There also aren't any known issues listed.
The obvious next step will be for Windows 10 build 17133 to be promoted to the Release Preview ring, before being pushed to production in a couple of weeks. At some point between now and then, Microsoft will also release at least one cumulative update for the new version, as that's also something that must be tested on a feature release. There will be new ISOs available at some point as well.
This is also the point where you might want to hop off of the Insider train. While receiving Fast ring builds, the only way to get off of the Insider Program is to reinstall a production version of Windows 10, or wait until the Insider Program and production align. Right now, they are aligned, so if you want to stop receiving builds without having to reinstall Windows, now is the time to do it, before new Redstone 5 builds show up.