Teardown specialist Chipworks has discovered that the iPhone 6s's SoC has been (prepare yourself...) dual-sourced:
It had been industry speculation prior to the iPhone 6S launch that Apple would be dual-sourcing the A9 and A9X from Samsung and TSMC, respectively. The A9 would have gone into iPhone 6S/6S+ and the A9X would have gone into iPad Pros, giving Samsung a large edge in volume for the A9 product family.
It was thus a surprise to find two different application processors in two otherwise identical iPhone 6S smartphones. As pictured below, there is a difference in the die size for the APL0898 (Samsung) and the APL1022 (TSMC).
Chipgate? Probably not, but why don't we all stop what we're doing right now to ID and benchmark our SoC's (editor: no, you don't need to do this, the performance differences between the two thus far appear to be less than 1%.).