Kohli has definitely breached the 900 icc ratings barrier after that innings, (may even go well past it,) so after the series it'll be reflected in his 'career best rating' figure, even though his rating by the end of the series may come back down below 900 if he doesn't perform in the coming games, which doesn't matter as much.
Since icc don't show updates after each match we may not get to see the 900+ figure at the end of the series but it will definitely show up in his career-best ratings column at the end of the series with Today's date on it.
900+ v South Africa, 07/02/2018
Only 11 other batsman have attained it, Tendulkar's best was 887. Of course ratings are not without their flaws but its good that finally an Indian player has gone past 900. This is not just an assumption, its 99% certain that after this game, he is beyond 900, and if India win, then its 100% guaranteed.
He was on 876 prior to series. And since then
-Match winning hundred in the 1st game vs No.1 team.
-Unbeaten innings in the 2nd game
-Unbeaten 160 potentially match winning innings in the 3rd game, scoring more than half of India's runs.
Could even go 910+ points depending on what kind of score South Africa put on.. and how other batsman fare on the wicket. Let's see.