Guilherme Rambo, 9to5Mac:

HomePod runs a special version of iOS, which means it gets new updates alongside iOS. The latest software publicly available for it is iOS 11.2.5, which will likely be the version installed on HomePods delivered on February 9th.

Software updates for HomePod will be managed through the Home app. The app will alert users when a new software update is available and will show an interface similar to the one used for iOS updates. Users will have the option to enable automatic updates, although it’s unclear how those will be managed. Updates can be installed on a single HomePod, all HomePods in the home or to specific stereo pairs (stereo pairing will not be available on HomePods running different software versions).

Interesting to me that there are a number of different update models at work here, all of them involving a satellite piece of Apple gear. Apple TV tends to update directly on device, Apple Watch has its own directly paired iOS device hosted Watch app, and now HomePod, which is part of the Home mini-ecosystem.

Seems to me like an opportunity for Apple to simplify their interface, make it a bit easier for beginners to master.