The Apple HomePod previously ran Apple’s iOS, according to a report from 9 to 5 Mac, this is something Apple ha changed recently and the device now runs on Apple’s tvOS instead of iOS.
According to the report when Apple released its most recent update for the HomePod, it is now running from tvOS 13.4.
Apple’s tvOS, watchOS and the HomePod OS are all based on iOS, there are then changes to each OS for each particular device.
Apple may have switched to the tvOS software for the HomePod in order to save themselves some time, the Apple TV and HomePod are similar devices, both are designed to be always on devices and have similar functions.
The HomePod is powered by an A8 processor, Apple may decide to stop supporting iPhones and iPads with the A8 processor when they release iOS 14 later this year, having the HomePod OS based on the tvOS would allow them to continue to support the HomePod and stop supporting other devices that use the same processor.
We recently heard a rumor that Apple will be launching a new smaller and cheaper HomePod later this year, this device is expected to launch with the iPhone 12 and iOS 14 later in the year, probably some time in September.
Source 9 to 5 Mac