Google is sending out an update to the Carrier Services app, although it isn't entirely clear what the app does exactly as the app description on the Play Store is mostly vague and according to some of the commenters on Reddit where this was pointed out, there doesn't seem to be a change in the code between this app version and the older app version. The Play Store listing for Carrier Services mentions that it helps provide mobile services with the most up to date networking capabilities. What exactly those networking capabilities are is not explained.
The app also lists that it includes support for enhanced services in the Android Messages app, which would be the stock text message app that comes on Android smartphones, which suggests that the update to carrier services has something to do with RCS messaging in some way, though it is worth mentioning that this does not enable RCS messages on phone that don't already have support, and it's not made clear how it enhances the support of RCS messaging on phones which are already compatible with the technology. The update is reported to be heading out to some users, and it seems to be on a global scale as users in various regions outside of the U.S. are noting that they have seen it pop up on their device.
It also seems to be hitting devices across a wide range of carriers including Project Fi, with at least one commenter on Reddit stating that they have seen it show up on their own device which is connected to the T-Mobile network. The Carrier Services app is also available to download and install from the Play Store and it isn't already installed on all devices, as it wasn't on my own personal Google Pixel but I was able to install it. For now the app seems to have no functionality and even the Play Store screenshots display that it just contains a dummy service at this point. That is likely to change though once Google throws out another update and flips the switch to enable whatever this app is meant to do, which suggests that it will eventually play a role in people's devices somehow.