iOS 9.0 (build 13A4325c) is an official Apple over-the-air update for the iPhone 4s, released on 2015-08-06T18:44:17Z. The update package is 237.5 MB. This is a delta (partial) update that requires 9.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c8161c0d93a5f1b918d5e207d8ab32fe82fdcdbc.zip.