Credible rumors point to the arrival of a brand new A9 processor for the iPhone 6s and iPhone 6s Plus.
The exact specs of the A9 chip are still shrouded in mystery though leading analysts believe that it will come backed by 2GB of RAM. The iPhone 6 and iPhone 6 Plus both utilize 1GB of RAM so this would be a huge change.
9to5Mac's Mark Gurman also believes that the iPhone 6s will come with a new Qualcomm chip that provides faster LTE data speeds and enhanced battery life.
Samsung and TSMC reportedly started production on the A9 in July, well ahead of the iPhone 6s release date, and at this point we wouldn't doubt a change to the CPU. Apple always swaps out an old processor in favor of a new one and that's precisely what you can count on this year with the iPhone 6s.