Was watching this live. Caruana had tremendous faith in his ability and judgement playing for a win to nick that b2 pawn.

If he had lost the 'I told you so crowd' (led by me and AylerKupp - in our day nobody ever took a QNP with a Queen, it was illegal.) and we would have come down on Caruana's head like a ton of Reinfeld books.

Zhang slipped in the good looking CGTN with 5.Qxd5 else we may have got:

K Nemcova vs V Zwardon, 2018

Where both players were seeing who would crack first to claim the three fold rep. (I think it was passed over nine 9 times. Could be wrong, I was running out of fingers.)

I do not think it was prep, unless Zhang used his clock time to disguise it. Let's go for OTB inspiration and balls of brass for saccing a pawn v the world's No.2.

Did not like Bxb8 though could see some reasons for it, thought Nf3, get castled ASAP and sac something was a plan.

The onsite Bomb computer says Black here...

click for larger view

...can play 37...Rxe4 but allowing 38.Rxd7+ It's is a defence best left to a computer which has no concept of time trouble. It's not a Queen for two Rooks game. (37....Rxd7+ 38.Qxd7) it ends with White playing Qd6+ then Qc6+ and picking up the loose e4 Rook.

Fabiano spent two precious minutes rejecting it and decided White gets too much OTB play for the piece, Zhang must have agreed because he was willing to sac it. In hindsight the correct decision.

That is a good spot, looks the CG opening database has not caught up with 5.Qxd4 yet, it still shows only 5.exd4 as being played.

Opening Explorer

The linked game has Qc1+ which is possibly the line Zhang was trying to get Caruana involved in.