Microsoft today released Windows 10 Insider Preview build 17134 to Insiders on the Fast ring today, replacing build 17133. The move is unprecedented, as it's the first time that a feature update as arrived in the Release Preview ring - which is designed for updates that will eventually arrive for non-Insiders - and has been replaced by a newer build due to a bug.
The blog post says that it includes the fixes from last week's cumulative update, and a few other reliability fixes that Microsoft wanted to hammer out.
Windows 10 build 17133 showed up in Release Preview a week ago, all but confirming that it's RTM. According to some reports, Microsoft was going to release it to non-Insiders on Tuesday, but that got delayed and the company ended up releasing a cumulative update, build 17133.73, to Insiders.
Also, keep in mind that Windows 10 build numbers align across the board, so with the Windows 10 release today, we can also expect build 17134 to arrive for the Xbox One and for HoloLens.
So it would seem that the delay on the Windows 10 spring feature update, or version 1803, is more than just a week. At this point, it seems like it might be closer to a few weeks, as Microsoft will have to test build 17134 with Insiders, and also test a cumulative update with it.
Nevertheless, Windows 10 build 17134 is the new RTM build for the spring feature update. Microsoft will certainly be announcing more about version 1803 over the coming days and weeks.