Turns out my hunches aren't always good, and Svidler did indeed lose game 4 of the match. He then compounded by this by losing the first game of today's rapid playoff making it three losses in a row, also known as 'Long Castling' (0-0-0). Currently they are playing the second rapidplay game (a must win for Svidler), and while Svidler is better at move 40, he may not be better enough.
Here is last nights games, which probably contains some important lessons. Firstly, the opening choice by Svidler was not that impressive (offering mass exchanges in the opening tend to favour the other player) while the endgame saw both a better pawn structure and RBvRN turning out better for Karjakin.
(Update: Svidler has just won the second game, tying the match up once again)
Karjakin,Sergey (2762) - Svidler,Peter (2727) [D02]
FIDE World Cup 2015 Baku AZE (7.4), 04.10.2015