iOS 6.1.6 (build 10B500) is an official Apple over-the-air update for the iPhone 3GS, released on 2014-02-21T18:09:15Z. The update package is 71.98 MB. This is a delta (partial) update that requires 6.0 already installed. This update is currently signed by Apple, so it can be applied from Settings › General › Software Update.

Payload file: e469e43836337624d0e5492d8c9d4afbe9b50b25.zip.