Usually, updates to the operating system of the HomePod (known as “audioOS”) come out of iOS because even what runs inside the smart speaker is nothing more than a subversion of iOS itself.
IOS 12.1 came out yesterday and in theory was for HomePod owners to have received an update as well, but it was only actually released today for everyone.
This update includes general stability and quality improvements.
As the release note indicates, there is no noticeable news in audioOS 12.1. The latest came in version 12.0, including searching for song lyrics, multiple definition timers, making calls, and Shortcuts support (Shortcuts) by Siri.
The update can be downloaded and applied immediately to HomePods by the Home app (Home) on both iOS and macOS.