iOS 8.4.1 (build 12H321) is an official Apple over-the-air update for the iPhone 4s, released on 2015-08-13T18:05:12Z. The update package is 824.9 MB. This is a delta (partial) update that requires 7.1.1 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: ac4c018475bd3cc7a222805412820bd4a712cd70.zip.