Apparently Qualcomm has been forced to delay the upgraded chipset until the beginning of next year. Snapdragon 836 is still likely coming, despite some other rumors.
So, 836: QCT had told GOOG to expect it, but then delayed it until early next year (tho perhaps under diff branding), forcing Pixels to 835.— Evan Blass (@evleaks) September 8, 2017
The Pixel duo is expected to become official on October 5.
If the differences between the Snapdragon 820 and 821 are anything to go by, the 836 shouldn't be a huge upgrade over the 835, so it's hardly a great loss. And Pixels are rarely lacking in performance so the current flagship chipset should do just fine.