audioOS 9.9.18.4 (build 22L255) is an official Apple over-the-air update for the HomePod (2nd generation), released on 2025-03-31T17:29:50Z. The update package is 1 GB. This is a delta (partial) update that requires 18.0 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: 90ca9406404acefab6fbcb2cb7ee16a36e1ad009acb81f541d711307448986dc.aea.