If you've been using the Windows Phone Developer Program to keep your phone up-to-date with the very latest in Windows Phone OS releases, you're used to the fact that Microsoft frequently updates the OS to a newer version. Likewise, you're used to the fact that many of these updates are undocumented and don't appear to change a thing. So that just happened.
To be more specific: If you have installed Windows Phone 8.1 Update 1 to your Windows Phone handset using the instructions I provided in Get Windows Phone 8.1 Update 1 Now, there is an update available now. This update will bump the OS version number to 8.10.14157.200.
I believe this is the first post-RTM update to Update 1. But there's no word about what's new in the release, which frankly isn't unusual, as Microsoft often updates Windows Phone OS releases after the RTM release. And I don't see any changes on my own phones, though I'll keep looking. (Let me know if you see anything unusual or different.) You may recall that Microsoft updated Windows Phone 8.1 several times after that release RTMd as well.
Thanks to WPCentral, I know that this update does not fix a common issue that some people have had upgrading to Update 1 through the Developer Preview program. This issue is described in a Microsoft support thread, and it's the one that throws up a "0x80188308 error" when you try to install Update 1. So if you do see that error, you'll need to wait a bit: Microsoft says it will fix that soon in another post-RTM update.
"As promised I want to make sure you folks are aware of what is going on," a Microsoft forum moderator explains. "We have a new update coming out today, however this update will not fix this specific error message. We are still working on this as a priority to get it out to you as soon as we can. We will continue to update this thread as we have more information."
Microsoft hasn't yet addressed another related issue that is preventing HTC 8X users from updating as well, to knowledge. It has said that HTC 8S users will not be getting the update.