audioOS 9.9.13.3 (build 17C54) is an official Apple over-the-air update for the HomePod, released on 2019-12-10T18:21:46Z. The update package is 1.48 GB. This is a delta (partial) update that requires 11.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 243ecb374b157926925a9bfde7cc4e54c4a1aec3.zip.